Optimizing vision correction procedures

ABSTRACT

In one embodiment, an apparatus for optimizing vision correction procedures comprising: a narrow beam of light directed to a patient&#39;s retina; a dynamic defocus and compensation offsetting device configured to offset the defocus of a wavefront from an eye, a wavefront sensor configured to measure the local tilt of a number of subwavefronts sampled around an annular ring (the diameter of which can be dynamically changed) over the wavefront with the defocus offset; and a display device configured to display a two dimensional (2D) data points pattern in real time with each data point location representing a corresponding local tilt of the sampled subwavefronts. A proper defocus offset, not passive compensation, can reveal the predominant feature(s) of other wavefront aberration component(s), thus enabling a refractive surgeon to fine tune the vision correction procedure and minimize the remaining wavefront aberration(s) in real time. Meanwhile, by sampling the wavefront around annular rings and displaying the local tilt of the sampled subwavefronts on a monitor in the form of a 2D data points pattern, a refractive ophthalmic surgeon can easily correlate the measurement result to the two major refractive errors, namely spherical and cylinder refractive errors, including the axis of astigmatism.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/761,890entitled Adaptive Sequential Wavefront Sensor, filed Jun. 12, 2007,which is a continuation of application Ser. No. 11/335,980 entitledSequential Wavefront Sensor, filed Jan. 20, 2006 now U.S. Pat. No.7,445,335, issued Nov. 4, 2008, all of which are incorporated byreference for all purposes.

TECHNICAL FIELD

One or more embodiments of the present invention relate generally toophthalmic wavefront sensors and adaptive optics systems. In particular,the invention is related to wavefront guided vision correctionprocedures.

BACKGROUND OF THE INVENTION

A wavefront sensor is a device for measuring the aberrations of anoptical wavefront. Wavefront sensors have been used for eye aberrationmeasurement by directing a narrow beam of light to the retina of an eyeand sensing the optical wavefront coming out from the eye. For a relaxedemmetropic eye or a relaxed eye with aberrations completely corrected,the optical wavefront coming out from the eye is planar. If, on theother hand, the eye has optical aberrations, the wavefront coming outfrom the eye in a relaxed state will depart from being planar.

Traditional vision diagnostic, vision corrective and surgical refractiveprocedures, including auto-refraction, standard eye wavefrontmeasurement, phoropter test, LASIK (Laser Assisted In-SituKeratomileusis), LTK (Laser Thermokeratoplasty), SBK (Sub-BowmansKeratomileusis), IntraLASIK (Intra-stromal corneal lenticuleextraction), PRK (photorefractive keratectomy), LASEK (Laser AssistedSub-Epithelium Keratomileusis), IOL (Intraocular lens, includingmulti-focal, accommodating and toric IOL) implantation, cornealonlay/inlay implantation/positioning, RK (Radial keratotomy), LRI(Limbal Relaxing Incision), CRI (Corneal Relaxing Incision), and AK(Arcuate Keratotomy), are generally conducted without any continuouswavefront measurement result being displayed in real time to theclinical practitioner to show the effect of the correction in real time(see for example U.S. Pat. No. 6,271,914, U.S. Pat. No. 6,271,915, U.S.Pat. No. 6,460,997, U.S. Pat. No. 6,497,483, and U.S. Pat. No.6,499,843). Although wavefront sensors have been used to measure therefractive errors and higher order aberrations of the eye before,during, and after the dynamic vision correction process, these devicesgenerally only produce a static snapshot display of the wavefront map ofthe measurement, thereby potentially missing information vital to thepractitioner for optimization of the optical outcome.

SUMMARY OF THE INVENTION

One example embodiment is an apparatus for optimizing vision correctionprocedures comprising: a narrow beam of light directed to a patient'sretina; a dynamic defocus offsetting device configured to offset thedefocus of a wavefront from an eye; a wavefront sensor configured tomeasure the local tilt of a number of subwavefronts sampled around anannular ring (the diameter of which can be dynamically changed) over thewavefront with the defocus offset; and a display device configured todisplay a two dimensional (2D) centroid data points pattern in real timewith each data point position representing a corresponding local tilt ofthe sampled subwavefronts.

Another embodiment is a method for optimizing vision correctionprocedures comprising: directing a narrow beam of light to a patient'sretina; dynamically offsetting the defocus of a wavefront from thepatient's eye; measuring with a real time wavefront sensor the localtilt of a number of subwavefronts sampled around an annular ring (thediameter of which can be dynamically changed) over the wavefront withthe defocus offset; and displaying a two dimensional (2D) centroid datapoint pattern in real time with each data point position representing acorresponding local tilt of the sampled subwavefronts.

Extending the general concept of offsetting some wavefront aberrationcomponents based on a real time wavefront measurement feedback to allowthe remaining aberration components to show up more clearly, oneembodiment is an apparatus for optimizing vision correction procedurescomprising: a narrow beam of light directed to a patient's retina; awavefront offsetting element configured to dynamically offset onlycertain aberration components of a wavefront from the patient's eye; areal time wavefront sensor configured to measure the local tilt of anumber of subwavefronts sampled according to a certain sampling patternover the wavefront with the offset; and a feedback means configured toguide the offsetting.

Another embodiment is a method for optimizing vision correctionprocedures comprising: directing a narrow beam of light to a patient'sretina; dynamically offsetting only certain aberration components of awavefront from the patient's eye with a wavefront offsetting element;measuring with a real time wavefront sensor the local tilt of a numberof subwavefronts sampled according to a certain sampling pattern overthe wavefront with the offset; and guiding the offsetting with afeedback means.

One aspect of the present invention is the active offsetting rather thana mere passive compensation of some wavefront aberration component(s)from an eye. The offset can be implemented using a simple focal lengthvariable lens or an equivalent, or a more complicated wavefrontmanipulator. A key differentiation from prior arts is the active part ofthe offsetting. The offset can be scanned and the deliberate offsettingcan be applied to one or more particular aberration component(s) in adynamic manner.

Another aspect of the present invention is the involvement of the enduser or the control of a built-in algorithm in determining the amount orrange of the offset to be applied based on the real time wavefrontmeasurement feedback. One purpose is to highlight the key features ofthose wavefront aberration components that need to be further correctedduring a vision correction procedure. Another purpose is to average outnoise and obtain a better measurement of the aberration of the eye.

Still another aspect of the present invention is the unique way tosample the wavefront and display the real time measurement result in amanner that a refractive surgeon can easily understand. In particular,by sampling around an annular ring of the wavefront with a certaindefocus offset or a scanning of the defocus offset, a 2D centroid datapoint pattern can be generated that can be fitted to an ellipse, with acircle and a straight line being the extreme case of an ellipse, and indoing so a direct representation of the sphero-cylindrical refractiveerrors can be achieved.

Still another aspect of the invention is to dynamically change theannular ring size selected for wavefront sampling so that while an easyto understand 2D centroid data point pattern is presented to the enduser, the sampling can also cover most of the wavefront if needed.Built-in algorithms can be used to take into consideration the annularring size change and to still present an ellipse or a diagram that is atypical representation of spherical and cylindrical refractive errors asis well understood by vision correction practitioners.

Still another aspect of the invention is to sample the wavefrontaccording to a sampling pattern while offsetting some lower orderaberrations so that information on some particular higher orderwavefront aberrations can be clearly highlighted or vice versa. Forexample, by dynamically offsetting defocus and compensating astigmatism,higher order aberration (HOA) content, such as coma, which is a veryprevalent HOA that surgeons are becoming familiar with and havetechniques to address surgically, can be highlighted and displayed in aformat easily understandable by clinical practitioners.

One object of the present invention is to guide IOL placementintra-operatively, and then confirm while still in the operating room,the optimal centration, tilt, circumferential angular orientation (inthe case of any lens with toricity), and refractive results (i.e. toconfirm emmetropia intra-operatively, or any other refractive endpointgoal for the patient). More specifically, the 2D centroid data pointpattern can be used to guide the reduction of tilt imparted by an IOL;when a multi-focal IOL is being implanted, the presently disclosedapparatus can be used to control and change the sampled annular ringsize to check the focus range of the implanted multi-focal IOL; when anaccommodative intra ocular lens (AIOL) is being implanted, the presentlydisclosed apparatus can be used to measure whether an implanted AIOL canprovide the desired accommodation range; when a toric IOL is beingimplanted, the presently disclosed apparatus can be used to guide thecentration and circumferential angular orientation positioning of thetoric IOL.

Another object of the present invention is to confirm if the opticalpower of the IOL selection is correct, especially for patients withpost-op corneal refractive procedures, for whom the pre-surgery IOLselection formulas do not deliver consistent results.

Still another object of the present invention is to shape and positioncorneal onlay and/or inlay ex-vivo or in-vivo.

Still another object of the present invention is to guide and optimizecorneal material removal based vision correction surgical proceduresusing the real time feedback with the offsetting property, such surgicalprocedures include LASIK, SBK, LTK, IntraLasik, FlEXi Lasik, PRK, LASEK,RK, LRI, CRI, and AK.

Still another object of the present invention is to confirm the aphakiccondition throughout the entire corneal visual field through dynamicallychanging the annular ring size

These and other features and advantages of the present invention willbecome more readily apparent to those skilled in the art upon review ofthe following detailed description of the embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows planar wavefront coming out from an emmetropic eye that isin a relaxed state.

FIG. 2 shows convergent spherical wavefront coming out from a myopic ornearsighted eye.

FIG. 3 shows divergent spherical wavefront coming out from a hyperopicor farsighted eye.

FIG. 4 shows the wavefront coming out from an eye that is nearsightedbut also with astigmatism.

FIG. 5 shows a schematic diagram of one embodiment in which a dynamicdefocus offsetting device is used to offset spherical refractive errorof the wavefront from an eye.

FIG. 6 shows a block diagram of a typical electronic control anddetection system that is illustrated in FIG. 5.

FIG. 7 shows an illustration of a surgical microscope with amicro-display incorporated at an object conjugate plane in the imagingpath.

FIG. 8 shows an example flow chart of a built-in algorithm that enablesthe scanning of defocus to determine the best defocus offset positionsthat can highlight the remaining aberration(s).

FIG. 9 shows a quad-detector with four photosensitive areas of A, B, C,and D, and the image spot on the quad-detector for a planar subwavefrontand a non-planar subwavefront.

FIG. 10 shows the sampling by a sequential wavefront sensor of a numberof subwavefronts around an annular ring of a planar wavefront, awavefront with defocus and a wavefront with astigmatism, the associatedimage spot position on a quad-detector and the sequential movement ofthe corresponding centroid positions when displayed on a monitor.

FIG. 11 shows the cross sectional wavefronts with different defocusoffset and the corresponding change of the 2D centroid data pointpattern for the case of an eye with only defocus or spherical refractiveerror.

FIG. 12 shows respectively the vertical and horizontal cross sectionalwavefronts with different defocus offset, and the corresponding changeof the 2D centroid data point pattern for the case of an eye with bothdefocus and astigmatism.

FIG. 13 shows an example flow chart of the major steps in finding themajor and minor axis, and thus the spherical and cylindrical refractiveerrors of the measured wavefront based on the 2D centroid data pointpattern.

FIG. 14 shows a schematic diagram of a toric lens that has axis marks.

FIG. 15 shows a schematic diagram of another embodiment in which adynamic wavefront manipulation device is used to offset some selectedaberration components of the wavefront.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Reference will now be made in detail to various embodiments of theinvention. Examples of these embodiments are illustrated in theaccompanying drawings. While the invention will be described inconjunction with these embodiments, it will be understood that it is notintended to limit the invention to any embodiment. On the contrary, itis intended to cover alternatives, modifications, and equivalents as maybe included within the spirit and scope of the invention as defined bythe appended claims. In the following description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe various embodiments. However, various embodiments may be practicedwithout some or all of these specific details. In other instances, wellknown process operations have not been described in detail in order notto unnecessarily obscure the present invention. Further, each appearanceof the phrase an “example embodiment” at various places in thespecification does not necessarily refer to the same example embodiment.

An eye without any optical aberration is called an emmetropic eye andthe normal aberration-free vision or sight is called emmtropia. In suchan eye with perfect vision, the rays of light from a distant object canbe brought into sharp focus on the retina while the eye is relaxed. Thisis what you want with laser or other vision correction procedures. Sincefor a distant object, the wavefront entering a relaxed emmetropic eyecan be considered planar, when the light ray propagation direction isreversed, i.e. when light rays emitted from a point source near thefovea travels backward through the eye optics system and leaves the eye,the wavefront is also planer. FIG. 1 shows the planar wavefront 110coming out from a relaxed emmetropic eye 120.

Eyes aberrations are traditionally classified as low order and highorder. Low-order aberrations include defocus (also called sphericalrefractive error) and astigmatism (also called cylindrical refractiveerror). More familiar names for two different types of defocus arenearsightedness (myopia) and farsightedness (hypermetropia orhyperopia). These refractive errors can be measured with anautorefractor, and they make up about 85 percent of all aberrations inan eye. When light rays emitted from a point source near the foveatravel backward through the eye optics system that has defocus andleaves the eye, the wavefront is either spherically convergent orspherically divergent. FIG. 2 shows the convergent spherical wavefront210 coming out from a myopic or nearsighted eye 220 and FIG. 3 shows thedivergent spherical wavefront 310 coming out from an hyperopic orfarsighted eye 320.

If there is no astigmatism, the cornea of the eye is shaped like thecross section of a baseball cut in half. The curvature or steepness ofthe half-dome is the same all the way around. Compare this to a corneawhich is similar to a football cut in half lengthwise (in the longdirection, through both pointy ends). The curvature of the cornea in thelong direction (along the seams) is not as steep as along the shortdirection. Such a cornea focuses light, not at a single point, but at 2points. Someone who has uncorrected astigmatism may see images that arefuzzy and doubled. A cornea shaped like a football, cut lengthwise, hasastigmatism.

In an eye with astigmatism, the rays of light from a distant object arebrought into focus along two perpendicular orientation directions at twodifferent points, for example, one on the retina and the other, behindthe retina. This can be the case of an eye with a cornea that hasastigmatism, a non-uniform curvature like the football cut lengthwise.The two different curvatures results in two different focal points.There are several different combinations of astigmatism, depending onwhere the focal points are located. Examples include:

Simple myopic astigmatism: One point in front of retina, the other onthe retina;

Compound myopic astigmatism: Both points of focus in front of theretina;

Simple hyperopic astigmatism: One point behind the retina, the other onthe retina;

Compound hyperopic astigmatism: Both points of focus behind the retina;

Mixed astigmatism: One point in front of the retina, the other behindthe retina;

Often, when astigmatism occurs inside the eye as well as at the cornea,the astigmatism inside the eye is just opposite in amount to the cornealastigmatism. The two forms of astigmatism can thus cancel each other andleave the eye with no significant amount of astigmatism.

An astigmatic eye generally has two different meridians, at 90° to eachother, which cause images to focus in different planes for eachmeridian. The meridians can each be myopic, hyperopic, or emmetropic.The correction for astigmatism is generally a cylindrical or toric lenswith different light ray focusing powers at different particularorientation directions.

Astigmatism causes images to be out of focus no matter what thedistance. It is possible for an astigmatic eye to minimize the blur byaccommodating, or focusing to bring the “circle of least confusion” ontothe retina.

In order to correct astigmatism, the location of the axis of acylindrical lens must be specified when it is placed before or insidethe eye. In designating the angle of the axis, the observer faces thepatient and the orientation angle zero is at the observer's left. Thescale is read below the horizontal line with 90° at the bottom and 180°at the right.

For the case of an astigmatic eye or an eye with cylindrical refractiveerror, the wavefront coming out from a point light source near the foveaof the eye will no longer be rotationally symmetric relative to theoptical axis and instead, the wavefront will have different sphericaldivergence or convergent along two different but mutually perpendicularazimuthal orientation directions.

FIG. 4 shows the wavefront coming out from an eye 420 that isnearsighted but also with astigmatism (compound myopic astigmatism).Note that the degree of convergence of the wavefront after leaving theeye is different for the vertical (side view) and the horizontal (topview) cross sections. The vertical cross sectional wavefront 410 a forthe side view case is initially more convergent after the light raysleave the eye than the horizontal cross sectional wavefront 410 b is forthe top view case. Correspondingly, the beam shape will also no longerbe purely conical with rotational symmetry around the optical axis. Asshown by the three-dimensional illustration of 430, following the lightpropagation from the right to the left, the beam cross-sectional shape(perpendicular to the beam propagation direction) will change from alarger horizontal ellipse, to a horizontal line, to a smaller horizontalellipse with a shorter major axis, to a circle of least confusion, to asmaller vertical ellipse with a shorter major axis, to a vertical line,then to a larger vertical ellipse. It should be noted that these shapesare for the beam cross sections that should not be confused with the twodimensional (2D) wavefront centroid data point pattern to be discussedbelow, although there is a correspondence or similarity between the two.

As for the wavefront, it is necessary to note that the geometric rayoptics representation is not accurate. As a beam gets focused near thebest focus position, wave optics should be used to figure out thewavefront changes. In fact, the beam behaves more like a Gaussian beamnear the best focus region and the curvature of the wavefront will notremain the same but will change gradually from a convergent wavefront toa slightly more convergent wavefront, then to a less convergentwavefront and finally to a planar one and then to a divergent wavefront.At the horizontal line beam shape position, the side view or verticalcross sectional wavefront is actually planar because this is the pointat which the corresponding vertical cross sectional wavefront ischanging from a convergent spherical wavefront to a divergent sphericalwavefront. Similarly, at the vertical line beam shape position, the topview or horizontal cross sectional wavefront will be planar because thisis the position at which the corresponding horizontal cross sectionalwavefront is changing from a convergent spherical wavefront to adivergent spherical wavefront. We will give a more detailed discussionon the correspondence between beam shape change and the associationwavefront change later.

It should be noted that visual acuity and visual performance are relatedto wavefront aberrations, but the metrics used to describe vision is notthe same as a glasses or contact lens prescription which can be taken toan optical shop to be filled. Vision is usually given in the Snellenformat, for example, 20/40. For 20/40 vision, an object that can be seenby a patient 20 feet away, can be seen from 40 feet away by someone whohas 20/20 vision. Therefore, someone with 20/400 vision has even worsevision; the larger the denominator or the second number, the poorer thevision. In the extreme, if the vision is even worse, such that a personcannot see the biggest letter “E” on the eye chart, the number offingers that can be counted is a way of measuring vision. If someone has“counting fingers at 3 feet”, it means the eye in question has worsethan 20/400 vision, and can only identify the number of fingers held 3feet away. The gold standard of perfect vision has been 20/20 vision,though there are patients capable of seeing better than “perfect”. Whilemost patients use both eyes together, vision is tested in each eyeseparately, as is the measurement of a person's prescription. The tablebelow shows the relationship between visual acuity (in feet and meters)and refractive error in diopters, which is a unit of measurement of theoptical power of a lens, equal to the reciprocal of the focal lengthmeasured in meters (that is, 1/meters).

Refractive Error Visual Acuity in Feet Visual Acuity in Meters inDiopters 20/20 6/6  0.00 20/30 6/9  −0.50 20/40 6/12 −0.75 20/50 6/15−1.00 20/70 6/20 −1.25  20/100 6/30 −1.50  20/150 6/45 −2.00  20/2006/60 −2.50  20/250 6/75 −3.00

In terms of prescription for vision correction, if an eye is justnearsighted, there will be a single negative diopter number. The minussign indicates nearsightedness or myopia. The number that comes afterthe minus sign tells the amount or “severity” of the nearsightedness.For examples a −1.00 D means one diopter of nearsightedness, a −5.25 Dmeans 5.25 or 5 and 1/4 diopters of nearsightedness. This is morenearsighted than −1.00 D, and so thicker negative glasses are needed.

If an eye is just farsighted, there will be a single positive diopternumber. The plus sign indicates farsightedness or hyperopia. The numberthat comes after the plus sign tells the amount or “severity” of thefarsightedness. For examples, a +1.00 D means one diopter offarsightedness, a +5.75 D means 5.75 or 5 and ¾ diopters offarsightedness. This is more farsighted than +1.00 D, and so thickerpositive glasses are needed.

If an eye has astigmatism, the numbers are harder to follow. There areactually 3 numbers in a prescription for an eye that has astigmatism.The general form is S+C×Axis. Both S and C can be either positive ornegative numbers. S refers to what is called the “sphere” or sphericalportion of the prescription. The C refers to the amount of astigmatismor cylindrical portion of the prescription. The Axis is a numberanywhere between 0 and 180 degrees; this axis number tells where thedifference in corneal curvature occurs or how the astigmatism isoriented or aligned. It is not enough to specify how much astigmatismthere is, it is necessary to know where the difference in curvature istaking place, by giving coordinates. Accordingly, there are threenumbers in a prescription for astigmatism of some kind and severity. Thebigger the second number, C, the more astigmatism there is. There areseveral categories of astigmatism, and by analyzing the 3-numberedprescription, the exact type of astigmatism is specified. For examples,−2.00+1.50×180 means a minus 2 diopter of spherical refractive errorwith a plus 1.50 diopter of astigmatism at an axis of 180 degrees;+4.00+3.00×89 means a plus 4 diopter of spherical refractive error witha plus 3 diopter of astigmatism at an axis of 89 degrees.

Higher-order aberrations refer to other distortion acquired by awavefront of light when it passes through an eye with irregularities ofits refractive components (tear film, cornea, aqueous humor, crystallinelens and vitreous humor). Abnormal curvature of the cornea andcrystalline lens may contribute to higher order aberrations (HOA).Serious higher-order aberrations also can occur from scarring of thecornea from eye surgery, trauma or disease. Cataracts clouding the eye'snatural lens also can cause higher-order aberrations. Aberrations alsomay result when dry eye diminishes eye's tear film, which helps bend orrefract light rays to achieve focus. Some names of higher orderaberrations are coma, trefoil and spherical aberration. Higher orderaberrations can be measured using a wavefront sensor and they make upabout 15 percent of the total number of aberrations in an eye.

In spite of the fact that wavefront sensors have been used to makemeasurement before a vision correction which can provide a prescriptionfor the vision correction procedure, and a snapshot of the wavefrontmeasurement result during or after the vision correction procedure cantell the vision correction practitioner if the correction is progressingor done properly, the static or snapshot nature of the wavefront mapcannot instantaneously guide or titrate the vision correction procedurein real time to optimize the vision correction outcome. The lack of realtime objective feedback often leads to the need for one or morefollow-up procedure(s) to trim or fine-tune the vision correction, whichis costly, inherently risky, time consuming and troublesome to both theeye doctor and the patient.

Even though there are disclosures on controlling laser based refractiveprocedures using wavefront measurement in a closed loop fashion (see forexample, U.S. Pat. No. 6,428,533, U.S. Pat. No. 6,887,232, U.S. Pat. No.7,232,463, U.S. Pat. No. 6,394,999, and U.S. Pat. No. 6,508,812) andalso on displaying the wavefront measurement result in real time (seefor example, U.S. Pat. No. 6,572,230, U.S. Pat. No. 6,609,794, and U.S.Pat. No. 6,631,991), the control and display are not user-friendlybecause the closed loop control does not give the clinical practitionerthe freedom to optimize the vision correction procedure in real time andthe display is not in a format that can be easily understood by thepractitioner. Furthermore, previous wavefront sensor based adaptiveoptics systems that have incorporated wavefront compensator(s) generallyoperate in an on/off manner to only allow the end user to turn thewavefront compensator(s) on or off to compensate some lower orders of orall of the aberrated eye wavefront (see for example, U.S. Pat. No.5,777,719, U.S. Pat. No. 5,949,521, U.S. Pat. No. 6,095,651, U.S. Pat.No. 6,948,818, U.S. Pat. No. 7,416,305, U.S. Pat. No. 6,595,643, U.S.Pat. No. 6,709,108, U.S. Pat. No. 6,964,480, U.S. Pat. No. 7,448,752,U.S. Pat. No. 7,419,264, U.S. Pat. No. 7,475,989, U.S. Pat. No.6,631,991, U.S. Pat. No. 6,634,750, U.S. Pat. No. 7,226,443, and U.S.Pat. No. 7,237,898). They do not allow the end user to dynamically orpartially cancel or deliberately offset some selected wavefrontaberration components to thus reveal important features of otherwavefront aberrations in a highlighted or pronounced manner. Inaddition, the traditional way to present the wavefront measurementresult, generally in the form of a 2D wavefront map or Zernikepolynomial coefficients is not at all easily understandable to visioncorrection practitioners or refractive surgeons. As such, clinicalpractitioners often find it difficult to interpret the wavefrontmeasurement for guidance during the vision correction procedure tooptimize the correction outcome.

In the following example embodiment are described that providecontinuous real time objective feed back of the wavefront measurement inthe form of a movie rather than a snap shot that is understandable to avision correction practitioner as the vision correction procedure is ongoing. This enables the vision correction practitioner to dynamicallyoffset or partially cancel only some wavefront aberration components inorder to highlight or even amplify the clinically important feature(s)of the remaining wavefront aberrations that need to be furthercorrected. Meanwhile, wavefront measurement result needs to be presentedin a manner that is easy to interpret and understand. Identification ofthese missed features will allow the vision correction procedure to bemore easily optimized in real time.

In accordance with one or more example embodiments, the defocuscomponent of a wavefront from an eye is offset deliberately andactively, either at the disposal of the end user or per some built-inalgorithms, in response to the real time feedback and/or the display ofthe measured wavefront. The deliberate and active offset is used notonly to serve the function of compensating the defocus of the wavefront,which can also serve the purpose of overcoming the dynamic range limitof the wavefront sensor in measuring the local tilt of a sampledsubwavefront, but also to show more clearly the predominant feature(s)of other wavefront aberration component(s), thus enabling the visioncorrection practitioner or the refractive surgeon to fine tune thevision correction procedure and minimize the remaining wavefrontaberration(s) in real time. In terms of sampling and displaying the realtime wavefront measurement result, sampling around an annular ringenables one to display the local tilt of the sampled subwavefronts on amonitor in the form of a 2D centroid data point pattern, which can befitted to a circle or an ellipse or a straight line, thus directlyindicating the two major refractive errors, namely spherical andcylindrical refractive errors, as well as the axis of thecylinder/astigmatism, or fitted to a cardioid for coma or other higherorder non-symmetrical forms. As a result, a refractive surgeon caneasily understand the wavefront measurement result and fine tune thevision correction accordingly.

Note that of all the wavefront aberrations, the spherical refractiveerror generally has the largest variation range (up to perhaps ±30diopters in some extreme cases) among different eyes, while all otherwavefront aberration components such as astigmatism generally have muchless variations. In addition, during a refractive surgery, if thecrystal lens in the eye is removed, the aphakic eye can have adrastically different spherical refractive error diopter value than thatof the phakic eye, with the difference being up to 20 diopters. Sincethe dynamic range of a wavefront sensor in terms of sensing the localtilt of a sampled subwavefront is limited, it is therefore desirable toarrange a defocus compensating device in the light path of the wavefrontsensor to just compensate for the spherical refractive error so that thedefocus compensated wavefront can be measured by the wavefront sensor.However, as mentioned before, prior art wavefront sensors with wavefrontcompensator(s) or adaptive optics systems basically all operate in an“on and off” format to either turn the wavefront compensation on or off.Such an operation does not provide enough help to a refractive surgeonin easily figuring out how the refractive correction should proceed inorder to achieve better vision correction in real time. To overcome thisshortcoming, the refractive surgeon or a built-in algorithm canselectively cancel or offset certain wavefront aberration component(s),thus enabling the remaining aberration(s) to be highlighted in a “zoomedin” or “magnified” manner. As a result, the refractive surgeon can seein real time how his/her vision correction procedure should proceed inorder to remove the remaining aberration(s), confirm the results, anddocument the value and sense of the compensated aberrations.

FIG. 5 shows one embodiment of a dynamic wavefront sensing system inwhich a defocus offset device is used to offset the spherical refractiveerror component of the wavefront from an eye.

A sequential wavefront sensor 528 has a first lens 504 that focuses alinearly polarized input beam of light having a wavefront 502. Thefocusing beam travels through a polarization beam splitter (PBS) 506,which is arranged in such a manner that its pass-through polarizationdirection is aligned with the polarization direction of the incomingbeam. As the result, the linearly polarized convergent beam will passthrough the PBS 506. A quarter-wave plate 508 is placed behind the PBS506 with fast axis oriented so that a circularly polarized beam isemerged after passing through the quarter-wave plate 508. A pinhole 510is placed behind the quarter wave plate 508 and right in front of thescanning mirror 512 to serve the purpose of rejecting the light notdirectly coming from interested wavefront of the light beam.

The input convergent beam, after passing through the pinhole 510, isfocused on the reflective surface of a tilted scanning mirror 512, whichis mounted on a motor shaft 514. The light beam reflected by the mirroris divergent, with its beam central chief ray changed to a directionthat is dependent on the tilting angle of the scan mirror 512 and therotational position of the motor 514. It is expected that the reflectedbeam is still circularly polarized, but the circular polarizationrotation direction will be changed from left hand to right hand or fromright hand to left hand. Hence, upon passing through the quarter-waveplate 508 for a second time on its return path, the beam becomeslinearly polarized again, but with its polarization direction rotated toan orthogonal direction with respect to that of the original incomingbeam. Therefore, at the polarization beam splitter 506, the returnedbeam will be mostly reflected to the left as shown by the dashed lightrays in FIG. 5.

A second lens 516 is placed on the left next to the PBS 506 to collimatethe reflected divergent beam and to produce a replica of the originalinput wavefront. Due to the tilting of the scan mirror, the replicatedwavefront is transversely shifted. An aperture 518 is placed behind thesecond lens 516 and right in front of the sub-wavefront focusing lens520 to select a small portion of the replicated wavefront. Thesub-wavefront focusing lens 520 focuses the selected sub-wavefront ontoa position sensing device 522, which is used to determine the centroidof the focused light spot generated from the sequentially selectedsub-wavefronts. By rotating the motor 514 and changing the tilting angleof the scan mirror 512 in a continuous or stepped fashion, the amount ofradial and azimuthal shift of the replicated wavefront can be controlledsuch that any potion of the replicated wavefront can be selected to passthrough the aperture 518 in a sequential way. As a result, the overallwavefront of the original incoming beam can be characterized as for thecase of a standard Hartmann-Shack wave-front sensor with the exceptionthat the centroid of each sub-wavefront is now obtained in a sequentialrather than a parallel manner

When the tilt angle of the scanning mirror remains constant an annularsection of the wavefront 502 is sequentially scanned. The radius of theannular section can be changed by changing the tilt of the scanningmirror.

The light source module 535, comprising the light source 534, thecollimating lens 537 and the beam directing element 536, is used todirect a narrow beam of light onto the retina of a patient eye 538. Ithas been mentioned in US20080278683 that the infrared imaging module 583can be used to monitor the position of the fovea and also to align andregister the eye. In addition, the internal fixation and visual acuityprojection module 542 as shown in FIG. 5 can comprise a micro display544, a variable focus lens 546 and a beam directing element 548, andserve the function of changing the accommodation of the patient's eye aswell as checking the patient's visual acuity. When the patient'saccommodative mechanism of the eye is not anaesthetized, a continuousmeasurement of wavefront aberrations over the full accommodation rangewill provide an optimized prescription for vision correction. In spiteof the fact that these two modules are shown, it should also beunderstood that they are not absolutely required for the apparatusembodiment.

However, as one aspect of an embodiment, the internal fixation/visualacuity projection module can also be used to change the accommodation ofthe patient's eye with wavefront measurements also done for the wholeaccommodation range. During accommodation, while the axis of fixationmay not change which means proper patient alignment, the actual visualaxis or center may vary, indicating a kind of pseudo accommodation ornon-symmetric visual correction. The wavefront sensor can record thevariation and determine accommodative correction.

As another aspect of an embodiment, the internal fixation/visual acuityprojection module can also be used to guide the patient to look off-axisso that the incident light beam can be guided to land on differentpositions of the retina rather then at the fovea region. This can beachieved by turning a certain pixel or group of pixels of the microdisplay 544 on and as a result, the eye will be directed to fixate onthe “on” pixel(s), making it possible to capture the eye aberrationwavefront for both the center and the peripheral light scatteringlocations. In doing so, wavefront aberrations can be measured as afunction of the landing position of the incident light beam andtherefore a 2D array of wavefront aberrations for light scattered fromdifferent locations on the retina can be generated. Such a 2D array ofwavefront measurements will provide a vision correction practitionerwith additional valuable information in addition to a conventional eyeaberration wavefront measurement resulting from only a central lightscattering location. This will further optimize aberration correctionprescriptions in the sense that in addition to central vision,peripheral vision can also be optimized.

In FIG. 5, active defocus offsetting is achieved by changing theeffective focal length or the spherical refractive power of a lens or alens combination 505 disposed in the optical path in front of awavefront sensor 528. The change of the effective focal length can becalibrated to indicate the correction in diopters (for example) requiredto change the actual wavefront returned from the retina to a plane wave.This correction in diopters is the refractive prescription forcorrecting the vision of a patient. The procedures for obtaining thisprescription for spherical and astigmatic aberrations are described indetail below.

Note that the difference between the current embodiment and thosedisclosed in U.S. Pat. No. 7,445,335 and US20080278683 is that a dynamicdefocus offsetting element 505 is arranged in the light path. Previousembodiments only mentioned the compensation or defocus nulling functionif such an element is used. In the current embodiment, in addition tothe compensation or nulling function, the defocus offsetting element 505also provides active off-setting or partial cancellation of thespherical refractive error component in either the positive or negativedirection to make the wavefront more or less spherically divergent orconvergent and the active offset is at the disposal of the refractivesurgeon or controlled by a built-in algorithm according to the real timedisplay and/or feedback of the wavefront measurement.

One aspect of the embodiment is to use the defocus offset device topartially compensate for any relatively large spherical refractive errorso that the remaining spherical and cylindrical refractive errors andother higher order aberrations all fall within the measurement dynamicrange of the wavefront sensor. As such, the variable focal length lensis functioning as an optical component that can also substantiallyincrease the measurement dynamic range of the combined wavefront sensingsystem. Another aspect of the embodiment is to scan the defocus offsetwithin the wavefront measurement range with or without the accommodationchange of the eye over the accommodation range so that a better and moreprecise measurement of the eye refractive errors can be obtained.

It should be noted that the defocus offsetting device described in FIG.5 can include a set of configured lenses to allow a shifting of thefocal range along the return beam optical axis. The position and axialspacing of these lenses provides an offset that can actively remove oradjust the spherical refractive error component of the transmitted beam.This active focusing alters the divergence or convergence of the beam to“fit” or allow matching of the beam focusing properties in order toaccentuate other aberration properties such as the appearance of theelliptically shaped beam pattern indicating an astigmatic condition.This “fitting process” does change the spherical power of such a beamwith an exact knowledge of the amount of compensatory focal change. Thefirst order linear focal shift introduced by the offsetting activelens(es) does(do) not alter the properties of the other inherentaberrations, it serves the basic purpose of highlighting and emphasizingthe underlying higher order aberrations that are present. Thesensitivity to detection of the existing higher order aberrationsincrease with more exact fitting location as the spherical refractiveerror component of the aberration is “matched” or “fitted” allowingbetter appreciation and detection of wavefront changes imposed by thelesser slope values which can be masked by large spherical wavefrontslope values.

This can be visualized by considering the appearance of the globe of theearth which has a larger base spherical shape with myriad small slopechanges caused by the local terrain changes with mountain ranges being apositive local slope change and valleys being a negative slope change.If one were to flatten out the large linear spherical component of theearth the remaining lesser slope changes would become increasinglyapparent as well as the better definition of the non-spheroid generalelliptical shape of the globe. This active defocus offsetting acts onlyon the linear spherical component of the collected returned beam.

It should be noted that although a positive plus negative lenscombination with relative axial movement is used as the defocusoffsetting element in FIG. 5, other focus variable optical element canbe used, including liquid or solid focus variable lenses, voice coil ormotor driven movable lens(es), liquid crystal lens(es), acousto-opticlens(es), deformable mirror(s) and diaphragm(s). The position of thedefocus offsetting element does not need to be right in front of thewavefront sensor and can be anywhere along the optical path as long asit serves the function of offsetting the defocus of the wavefront. Infact, for a compact design the defocus offsetting element can bedesigned together with other optical element(s) inside the wavefrontsensor 528. For example, it can be combined with the front focusing lens504 of the sequential wavefront sensor 528. Such a real time sequentialwavefront can be made with a small form factor and thus be integratedinto a large number of optical imaging or measurement systems, such asan eye refractive surgical microscope. It should also be noted thatalthough a sequential wavefront sensor 528 has been illustrated in FIG.5, other types of wavefront sensors can also be used as long as it canprovide wavefront measurement, including Hartmann-Shack, Talbot-Moire,Tscherning, Ray-tracing, phase diversity and interferometric wavefrontsensors.

The electronic control and detection system 532 coordinates theactivation of all active elements, including the defocus offsettingdevice 505, the focusing lens 582 of the near infrared imaging camera584, the accommodation changing element 546 of the internalfixation/visual acuity projector 542 and others.

FIG. 6 is a detailed block diagram of an example embodiment theelectronic control and detection system 532. A printed circuit board(PCB) 600 includes a micro-controller 601 having a memory 602 forstoring program code and data, and a processing unit 604 for executingthe program code and processing the data. The microcontroller has an I/Ointerface (indicated by arrows) 605 coupled to various control modules606 to 618. The control modules are interfaced with the variouscomponents of the deterministic dynamic wavefront sensing systemdepicted in FIG. 5 using standard techniques.

The PCB 600 also includes a host-side interface 620 for interfacing withthe host computer and display module 592 and a user interface 622 forinterfacing with a user interface device such as a foot pedal 624. Thefoot pedal can be configured to allow a surgeon to “zoom in” or “zoomout” by controlling the position of the defocusing mechanism.

The memory 602 is configured to store programs executed to perform thealgorithms described below to control the deterministic dynamicwavefront sensing system depicted in FIG. 5. The various modulesdepicted in FIG. 6 may be implemented as discrete parts or integratedonto ASICs or other programmable devices.

The microcontroller 601 can send control signal to a scanning mirrorcontroller connected 606 to a scanning mirror driver to drive thescanning mirror 514 and can send control signals to a light sourcecontroller 608 to turn the light source 534 on and off. Further, themicrocontroller can receive signals from the quadrant detector 522 asshown in FIG. 5 through a front-end amplifier and an A/D converter 610.In addition, the microcontroller can also control the NIR camerafocusing lens 582 through a focus lens controller 612. One key functionof the microcontroller is to offset the defocus of the defocus offsetdevice 505 through a defocus offset controller 614. More additionalfunctions that the microcontroller can provide include changing theaccommodation of the patient eye by controlling the accommodationchanging element 546 through an internal fixation controller 616, andchanging the subwavefront sampling aperture size of the variableaperture device 518 through a variable aperture controller 618. Thefunction of the electronic control and detection sub-system can beprovided by a dedicated micro-processor or a computer or otherelectronic processing means and therefore, the electronic control anddetection system 532 shown in FIG. 5 should only be considered as anoptional component but not as an absolutely needed item for theapparatus.

The display module 592 shown in FIG. 5 is included because it can beviewed directly by a refractive surgeon during a vision correctionprocedure to guide him/her in selecting the desired defocus offset andin optimizing the vision correction outcome. It should, however, benoted that the display module 592 in FIG. 5 should be interpretedbroadly as a real time feedback means. In fact, for a vision correctionsurgical procedure under a surgical microscope, an approach to implementthe display of the real time wavefront measurement is to incorporate amicro display inside the surgical microscope so that the wavefrontmeasurement result can be overlaid onto the image of the patient's eyeformed by the surgical microscope and presented to the refractivesurgeon directly. In doing so, the surgeon does not need to move his/herhead away from the binocular of the surgical microscope.

FIG. 7 shows an illustration of a surgical microscope 710 with asemi-transparent micro-display 720 incorporated at an object conjugateplane in the imaging path. This micro-display is utilized to display theoutput of the deterministic dynamic wavefront sensing system of FIG. 5so that the surgeon can respond to information provided without havingto glance away from the microscope eyepiece. It should be noted that ifthe micro-display is not semi-transparent, a beam directing element canbe arranged in the imaging path to enable the projection of themicro-display image onto the retina of a surgeon's eye. The display canalso be a small LCD monitor that is mounted directly onto a surgicalmicroscope.

On the other hand, if the surgical microscopic view is already shown ona large screen away from the surgical microscope and the surgeon isoperating on the patient according to the large screen displayedmicroscopic view, the real time wavefront measurement result should thenbe preferably shown on the same large screen either as an overlaid imageor separately on a different display window.

The information provided by the real time wavefront measurement with thedefocus offset can also be in other data format. One example is the useof a built-in algorithm that will automatically offset or scan thedefocus and at the same time inform the refractive surgeon that he/sheshould continue the vision correction procedure in a certain manner.

FIG. 8 shows an example flow chart of such a built-in algorithm in whichthe defocus is scanned to determine the best defocus offset positionsthat can highlight the remaining aberrations. The defocus offset settingvalue or position is then selected and the refractive surgeon isinstructed on how he/she should continue the vision correctionprocedure.

In process block 800 a wavefront processor real time feedback algorithmis initiated. For example, a user could select the real time feedbackalgorithm from a menu of algorithms displayed on the display of thehost.

In process block 802 the defocus offset is moved to the next positionand in process block 804 the responses from the image spot positiondetector quadrants are measured.

In process block 806 the Cartesian coordinates based on the responsefrom each position detector quadrant are computed. Then, for example,wavefront tilts, the centroid locations, major and minor axes, themagnitudes of sphero, cylindrical, coma and trefoil aberrations of thesampled wavefront are determined. Also, the centroid trace is displayed.The computation can be done for the same defocus offset position amultiple number of times until for example, a desired signal to noiseratio is reached through averaging and in other words, the same annularring can be sample a multiple number of time and averaging is done untilthe desired signal to noise is obtained. Also, a number of concentricannular rings can be sampled to cover the whole wavefront. In addition,the number of sub-wavefronts that one wants to sample around a singleannular ring can also be changed by firing the light source in pulsemode a multiple number of times in synchronization with the scanning ofthe scan mirror.

In process block 810 it is determined whether the required number ofdefocus offset data points have been collected. If the required ordesired number of data points is not reached, the processing returns toprocessing block 802, the defocus is offset to the next position. Todetermine if the required or desired number of data points is notreached or not, one can used the real time wavefront measurement resultas a criterion. If the wavefront measurement indicates that the sampledsub-wavefront tilt is still within the dynamic range of the wavefrontsensor, the defocus offset can continue. If the on the other hand, thewavefront sensor measurement result shows that the one or more measuredsub-wavefront local tilt is already at or outside its dynamic range,this will indicate that one end of the defocus offset is reached. Thesame criterion can be used to determined the other end of the defocusoffset until all data points within the two extremes are collected.

If the answer to the question on whether required or desired number ofdata points is reached is yes, then processing proceeds to processingblock 812 where, from the ellipses obtained by scanning the offset, thebest offset value(s) is(are) determined that can highlight remainingaberrations. This step is described in detail below with reference toFIG. 13. The defocusing mechanism is offset to one of the “best offset”values and the resulting centroid data points are displayed on adisplay. Information is provided to a refractive surgeon on how to bestcontinue a vision correction procedure.

For example, the information, such as which direction to move an IOL forproper alignment or which direction to rotate a toric lens to correctastigmatism, could be provided as graphic information or text on thedisplay.

This instruction does not have to be in a visual display format becauseother forms of feedback such as audio instruction can also serve thesame function. In other example embodiment, the visual display modulecan be replaced by a general feedback mechanism which can be embedded inthe electronic control and detection system 532. It is also possiblethat both a visual display and an audio instruction can be combined toguide the surgeon in completing the vision correction procedure.

The wavefront sensor real-time feedback algorithm can be implementedautomatically by the microcontroller executing firmware held in onboardmemory. Alternatively, the program code could be stored on the host andused to control the various control modules or some combination of hostcontrol and firmware could be utilized.

During a vision correction procedure, a goal is to improve the patient'svision to the point of an emmetropic state. To achieve this, low-orderand high-order optical aberration errors, such as sphere, cylinder,trefoil, and coma require correction. Traditional correction occursthrough a static measurement with a resultant number, typically indiopters, indicating the amount of optical refractive error andcorrection or nulling required. The correction is applied and anotherstatic measurement is taken to determine the effectiveness of thetreatment or correction.

With the advent of presently disclosed real time wavefront measurementapparatus, not only can the dioptric values of optical aberrations bedisplayed real time, but an audio signal can also be provided real timeto indicate the type of error, magnitude of error, and change in error.The audio feedback can consist of pitch, tone and loudness and can varyindividually or collective, as examples. The audio feedback can varyhigh to low as the applied correction improves the error; conversely, ifthe applied correction worsens or adversely alters the error, the audiofeedback can vary from low to high. In the advent that the user is hardof hearing, for example, the ascent and descent of the audio can bereversed.

An embodiment of audio feedback for correction of cylinder error couldconsist of a specific pitch identifying the error as cylinder with atone that indicates the magnitude of the error. As the correction isapplied, in this example a toric IOL is rotated, the pitch would ascendor descend (frequency would increase or decrease) whether the correctionis converging toward an emmetropic state (nulling the inherent cylindererror with the IOL) or diverging. Once the desired correction isachieved a different pitch and or tone could be transmitted forconfirmation or the user could listen for the transition point ofascending to descending sound.

This audio feedback, can be applied to all corrective procedures whetherintraoperatively or corrective spectacles, etc. In providing this audiofeedback, the clinician would not have to lift their head or diverttheir eyes from the correction procedure or surgery, thus minimizingpotential for errors. This real time audio feedback can be applied toany application of wavefront in the detection, measurement, and/orcorrection of wavefront error.

It has been mentioned in U.S. Pat. No. 7,445,335 that by sampling awavefront around an annular ring and displaying a 2D data point patternwith the location of each data point representing the local tilt interms of centroid position of the sampled subwavefront, the centroidposition 2D data point pattern can directly indicate, in real time,whether the wavefront is planer or not, how far off the defocus is,whether the defocus is convergent or divergent, what the amount ofastigmatism is, and where the axis of astigmatism is.

To illustrate the points, we will briefly repeat what has been discussedin U.S. Pat. No. 7,445,335. Assume that a sequential wavefront sensor928 is used for wavefront sampling and a quad-detector 922 with fourphotosensitive areas of A, B, C, and D is used to indicate the localtilt in terms of the centroid position of the sampled subwavefront imagespot position as shown in FIG. 9. If the subwavefront is incident at anormal angle with respect to the subwavefront focusing lens 920 in frontof the quad-detector 922, the image spot 934 on the quad-detector 922will be at the center and the four photosensitive areas will receive thesame amount of light, with each area producing a signal of the samestrength. On the other hand, if the subwavefront departs from normalincidence with a tilting angle (say, pointing toward the right-upperdirection), the image spot on the quad-detector will then be formed awayfrom the center (moved towards the right-upper quadrant as shown by theimage spot 936).

The departure (x, y) of the centroid from the center (x=0, y=0) can beapproximated to a first order using the following equation:

$\begin{matrix}{{x = \frac{( {B + C} ) - ( {A + D} )}{A + B + C + D}}{y = \frac{( {A + B} ) - ( {C + D} )}{A + B + C + D}}} & (1)\end{matrix}$

where A, B, C and D stand for the signal strength of each correspondingphotosensitive area of the quad-detector and the denominator (A+B+C+D)is used to normalize the measurement so that the effect of opticalsource intensity fluctuation can be cancelled. It should be noted thatEquation (1) is not perfectly accurate in calculating the local tilt interms of the centroid position, but it is a good approximation. Inpractice, there may be a need to further correct the image spot positionerrors that can be induced by the equation using some mathematics and abuilt-in algorithm.

When a number of symmetric sub-wavefronts (for example, 4, 8 or 16)around an annular ring of an optical beam is sequentially sampled andhence projected (for example, in a clockwise direction) onto thesub-wavefront focusing lens 920 and quad-detector 922, the departure ofthe centroid as indicated by (x, y) of Equation (1) from the center ofthe quad-detector will trace a pattern on an x-y coordinate that can bedisplayed on a monitor and also be processed digitally to represent thestatus of defocus and astigmatism as well as non-symmetry.

FIG. 10 shows a number of representative cases of planar wavefront,defocus and astigmatism, the associated image spot position on thequad-detector behind the subwavefront focusing lens, as well as thesequential movement of the corresponding centroid positions whendisplayed as a 2D data point pattern on a monitor. Note that instead ofdrawing a number of shifted wavefronts being sampled and projected asdifferent subwavefronts onto the same subwavefront focusing lens and thequad-detector, we have taken the equivalent representation such that anumber of subwavefronts are drawn around the same annular ring andaccordingly, a number of quad-detectors are drawn around the sameannular ring to represent the case of scanning different portions of awavefront to a single subwavefront focusing lens and a singlequad-detector.

Assume that we start the scan around the wavefront annular ring from thetop subwavefront and move in a clockwise direction to the secondsubwavefront on the right and so forth as indicated by the arrow 1009.It can be seen from FIG. 10 that when the wavefront is a plane wave1001, all the subwavefronts (for example, 1002) will form an image spot1003 at the center of the quad-detector 1004 and as a result, thecentroid trace 1005 on a monitor 1006 will also be always at the originof the x-y coordinate.

When the input wavefront is divergent as shown by 1011, the center ofthe image spot 1013 of each subwavefront 1012 will be on the radiallyoutward side from the wavefront center with an equal amount of departurefrom the center of the quad-detector 1014, and as a result, the trace1015 on the monitor 1016 will be a clockwise circle as indicated by thearrow 1018 starting from the top position 1017. If, on the other hand,the input wavefront is convergent as shown by 1021, the center of theimage spot 1023 of each subwavefront 1022 will be on the radially inwardside relative to the center of the wavefront with an equal amount ofdeparture from the center of the quad-detector 1024. As a result, thecentroid trace 1025 on the monitor 1026 will still be a circle but willstart from the bottom position 1027 and will still be clockwise asindicated by the arrow 1028. Hence when a sign change for both thex-axis centroid position and the y-axis centroid position is detected,it is an indication that the input wavefront is changing from adivergent beam to a convergent beam or the other way round. Furthermore,the starting point of the centroid trace can also be used as a criterionto indicate if the input wavefront is divergent or convergent.

It can also be seen from FIG. 10 that when the input wavefront isastigmatic, it can happen that the wavefront can be divergent in thevertical direction as shown by 1031 a and convergent in the horizontaldirection as shown by 1031 b. As a result, the centroid position of thevertical subwavefronts 1033 a will be located radially outward withrespect to the center of the input wavefront, and the centroid positionof the horizontal sub-wavefronts 1033 b will be located radially inwardwith respect to the center of the input wavefront. Consequently, thecentroid trace 1035 on the monitor 1036 will start from the top position1037 but move anti-clockwise as indicated by arrow 1038, hence thecentroid trace rotation is now reversed.

Using a similar argument, it is not difficult to figure out that if theinput wavefront is astigmatic but all the subwavefronts are eitherentirely divergent or entirely convergent, the rotation of the centroidtrace will be clockwise (i.e. not reversed), however, for the astigmaticcase, the trace of the centroid on the monitor will be elliptic ratherthan circular since the subwavefronts along one astigmatic axis will bemore divergent or convergent than those along the other axis.

For a more general astigmatic wavefront, either the centroid trace willrotate in the reversed direction with the trace either elliptical orcircular, or the centroid trace will rotate in the normal clockwiserotation direction but the trace will be elliptical. The axis of theellipse can be in any radial direction relative to the center, whichwill indicate the axis of the astigmatism. In such a case, 4subwavefronts around an annular ring may not be enough in preciselydetermining the axis of the astigmatism and more subwavefronts (such as8, 16 or 32 instead of 4) can be sampled around an annular ring.

As mentioned in the summary section, one novel feature of theembodiments is the way the wavefront is sampled and the wavefrontmeasurement result is displayed. Although in U.S. Pat. No. 7,445,335, ithas been mentioned that by sampling a number of subwavefronts around anannular ring of the wavefront from a patient's eye, the spherical andcylindrical refractive errors (or defocus and astigmatism) of the eyecan be determined, there was no detailed explanation about the effect ofactively offsetting the defocus on the 2D data point pattern. If the eyehas a relatively large spherical refractive error and a relatively smallastigmatism, the 2D centroid data point pattern will look more like acircle with its ellipticity hardly visible and this will make it hard todetect the axis of the astigmatism as well as the amount of theastigmatism. On the other hand, if the defocus of the original wavefronthas a proper offset, the remaining astigmatism can be made to clearlyshow itself up in the 2D data point pattern, clearly indicating the axisand the amount of the astigmatic error.

FIG. 11 shows the meridianal cross sections of the wavefront withdifferent defocus offset and the corresponding change of the 2D datapoint pattern for the case of an emmetropic eye or an eye with onlyspherical refractive error. In FIG. 11 a top row of wavefront drawings1112 to 1116 depicts the curvature of the wavefront for a particulardefocus offset and the part of the detector upon which an image spot ofthe sub-wavefront is focused by a lens. A middle row of drawings shows aring of detectors oriented to detect the focused image spot ofsub-wavefronts of an annular portion of the wavefront and the offsets ofthe wavefront centroids from the center (x=0, y=0) of the detectors. Abottom row depicts the departure of each centroid on each detectorquadrant displayed relative to an origin corresponding to (x=0, y=0).The letter labels on the displayed data points of the display correspondto the labels of the detectors in the ring of detectors.

In FIG. 11, the wavefront illustration, detector illustration anddisplay illustration for a single defocus offset are arrangedvertically. For example, for the defocus offset 1112, the detectors andimage spots are depicted in 1132 and the display in 1122.

It can be seen that as the defocus offset is tuned (from left to right),the resultant wavefront will change from a spherically more divergentwavefront 1112, to a spherically less divergent wavefront 1113, to aplanar wavefront 1114, to a spherically less convergent wavefront 1115,and to a spherically more convergent wavefront 1116. Correspondingly,the image spot position on quad-detector will also change as shown inFIG. 11 from radially more outward 1132, to radially less outward 1133,to landing at the center 1134, to radially less inward 1135, to radiallymore inward 1136. In accordance, the 2D data point pattern will alsochange from a larger circle 1122 with data point “a” at the firstquadrant, to a smaller circle 1123 with data point “a” still at thefirst quadrant, to a centered collection of the data points 1124, to asmaller circle 1125 with data point “a” now at the third quadrant, andthen to a larger circle 1126 with data point “a” still at the thirdquadrant.

One feature associated with sequential sampling of the subwavefrontsaround an annular ring is that, regardless of whether the resultantwavefront is spherically divergent or convergent, the sequence of the 2Ddata points displayed will follow a certain rotation direction (as shownby the sequence of a, b, c, d in FIG. 11). However, the position of thedata points will be on the opposite side of the circular centroid traceif there is a change in the divergence or convergence of the sphericalwavefront. Therefore the location of the data points relative to thecenter of the circle can tell if the wavefront is divergent orconvergent.

As one aspect of an embodiment, a calibration wavefront measurement canbe made for a substantially planar wavefront to determine therelationship between the centroid trace diameter, the annular ringdiameter and/or width, and the defocus offset. Then a real measurementof a wavefront from an eye can be made by scanning the defocus offset,also possibly the annular ring size in terms of its diameter and width,and relating the measurement results to the calibration data. In doingso, a more accurate measurement of the spherical refractive error of aneye can be obtained.

Additionally, FIG. 11 actually also shows a phenomenon that can be usedfor alignment. Note that the center of the 2D data point pattern orcentroid trace circle actually moved as the defocus offsetting elementis scanned. This can be caused by a misalignment of the optical axisbetween the wavefront sensor and the defocus offsetting element, or itcan be caused by a lateral or transverse movement of the eye when thedefocus offsetting element is tuned or scanned. Therefore, as one aspectof an embodiment, this phenomenon can be used to align the defocusoffsetting device with the wavefront sensor. As another aspect of anembodiment, the real time wavefront sensor with active defocusoffsetting element can also be used to indicate the alignment of the eyerelative to the presently disclosed apparatus.

In addition, the apparatus can also be used with the real time displayof the 2D data point pattern to guide the end user in aligning thepatient's eye with the apparatus. Furthermore, it can also be used foreye tracking. The defocus offset can be properly selected so that adesired 2D data point pattern with a proper dimension can be obtainedand a built-in algorithm can be used to extract the center position ofthe 2D data point pattern and drive a mechanical mechanism to move theapparatus relative to the patient eye in a closed loop fashion so thatthe eye is always aligned with the apparatus. Another aspect of thisfeedback position for alignment is to implement a real time correctingalgorithm that updates the data with respect to correcting the shiftedcoordinates measured and actively displays the properly aligned data.

It should be noted that although in FIGS. 9, 10, and 11, the origin ofthe x-y coordinate is used as the reference point. This is only onespecial case. In fact, if the quad-detector is not axially aligned withthe optical axis of the subwavefront focusing lens, the image spot of aplanar subwavefront will not be equally shared by the 4 quadrants. If,in this case, the overall wavefront is planar, all the samplesubwavefronts will still be planar and hence all the centroid data pointlocation will be the same. In other words, when the overall wavefront isplanar, the 2D centroid data points will collapse to the same positionwhich does not need to be the origin of the x-y coordinates. So apractical approach for alignment of the patient eye or the defocusoffset device relative to the wavefront sensor is to use a referenceplanar wavefront to identify this reference point on the x-y coordinateand then to use a built-in algorithm to indicate if the measuredwavefront, either from the patient eye or after passing through someoptical element such as the defocus offsetting device, is alignedrelative to this reference point

FIG. 12 shows, for the case of an eye with both defocus and astigmatism,the vertical and horizontal cross sectional wavefronts with differentdefocus offsets, the corresponding image spots of the sampledsubwavefront on the quad detector, and the corresponding change of the2D data point pattern.

FIG. 12 is organized the same as FIG. 11 except that vertical andhorizontal sections of the wavefront are now depicted because in thecase of astigmatism those sections will have different curvatures asdescribed above with reference to FIG. 4.

As described above, the Axis of astigmatism is a number anywhere between0 and 180 degrees; this axis number tells where the difference incorneal curvature occurs or how the astigmatism is oriented or aligned.In both FIG. 4 and FIG. 12 the Axis is either a vertical line or ahorizontal line to facilitate clear description. However, as known inthe art, the axis can have other values for the actual eye beingmeasured.

As the defocus offset is tuned as shown in FIG. 12 (from left to right),the vertical cross sectional wavefront 1212 is initially more divergentthan the corresponding horizontal cross sectional wavefront.Correspondingly, the image spots on quad-detector as shown by 1242 willbe more radially outward for those subwavefronts sampled at the top andbottom portion of an annular ring (a and c) than those sampled at theleft and right portion of the annular ring (d and b). As a result, the2D centroid data point pattern 1232 will be an ellipse with the majoraxis aligned substantially vertically.

With the defocus offset tuned further, the vertical cross sectionalwavefront 1213 becomes less divergent while the corresponding horizontalcross sectional wavefront 1223 is planar. Therefore, the image spots onquad-detector as shown by 1243 will be less radially outward for thosesubwavefronts sampled at the top and bottom portion of an annular ring(a and c), while the image spots of those subwavefronts sampled at theleft and right portion of the annular ring (d and b) will landsubstantially close to the center of the quad-detector. As a result, the2D centroid data point pattern 1233 will substantially resemble avertical line.

With the defocus offset tuned further, the vertical cross sectionalwavefront 1214 can become even less divergent with a degree ofdivergence that is equal to the degree of convergence of the horizontalcross sectional wavefront 1224 that has passed the planar wavefrontpoint and changed from divergence to convergence. Correspondingly, theimage spots on quad-detector (a and c) as shown by 1244 will be evenless radially outward for those subwavefronts sampled at the top andbottom portion of an annular ring while those image spots forsubwavefronts sampled at the left and right portion of the annular ring(b and d) will now be somewhat radially inward with the inwardness equalto the outwardness of the image spots of those subwavefronts sampled atthe top and bottom portion. As a result, the 2D centroid data pointpattern 1234 will resemble a circle with reversed rotation sequence asdiscussed before.

With the defocus offset still tuned further, the vertical crosssectional wavefront 1215 now becomes planar while the horizontal crosssectional wavefront 1225 becomes more convergent. Correspondingly, theimage spots on quad-detector as shown by 1245 will land close to thecenter for those subwavefronts sampled at the top and bottom portion ofan annular ring (a and c) while for those subwavefronts sampled at theleft and right portion of the annular ring (b and d) the image spotswill be more radially inward. As a result, the 2D centroid data pointpattern 1235 will resemble a horizontal line.

With the defocus offset tuned even further, the vertical cross sectionalwavefront 1216 will have passed the planar point to become slightlyconvergent while the horizontal cross sectional wavefront 1226 nowbecomes even more convergent. Correspondingly, the image spots onquad-detector as shown by 1246 will be radially slightly inward forthose subwavefronts sampled at the top and bottom portion of an annularring (a and c) while for those sampled at the left and right portion ofthe annular ring (b and d) the image spots will be even more radiallyinward. As a result, the 2D centroid data point pattern 1236 willresemble a horizontal ellipse.

It can be seen from FIG. 12 that when the degree of ellipticity issmall, it will be more difficult to precisely determine the major andminor axis of the ellipse and the amount of ellipticity both of whichrelate to the astigmatic refractive error. Similar to the pure defocusor spherical refractive error case, the sequence of the 2D data pointpattern, although now resembling an ellipse, will follow a certainrotation direction if the subwavefronts are sampled sequentially aroundan annular ring. Again, the location of each data point will be on theopposite side relative to the center of the ellipse if there is a changein the overall divergence or convergence of the resultant wavefront. Soif the rotation of the centroid trace is not reversed, the location ofthe data points relative to the center of the ellipse can tell if theoverall wavefront is divergent or convergent. Meanwhile the shape of theellipse in terms of the major and minor axis orientation, the major andminor axis length and the ratio of the major axis length over the minoraxis length or the ellipticity can all be used to tell the degree of themeasured astigmatism.

However, when the defocus offset is tuned towards a better compensationof the defocus component, the resultant wavefront will change in such away that the overall divergence or convergence will decrease until alonga particular direction on the resultant wavefront, the local tiltbecomes zero i.e. the associated cross sectional wavefront becomesplanar as shown by 1223 and 1215. The corresponding two straight linesof the 2D centroid data point patterns (1233 and 1235) will beperpendicular to each other if there are no higher order aberrationsexcept for defocus and astigmatism. As the defocus offsetting device isfurther tuned towards an even better compensation of the defocuscomponent, the result wavefront will have a larger portion moredivergent and a smaller portion less convergent or the other way round.The 2D data point patterns for such a case are not shown in FIG. 12, butit can be envisioned based on our discussion made so far. One feature ofthe 2D data point pattern for now is that the sequential rotation of thecentroid trace will be reversed and the data point pattern will resemblea smaller ellipse with a shorter major axis. Again the shape of thesequentially reversed ellipse in terms of the major and minor axisorientation, the major and minor axis length and the ratio of the majoraxis length over the minor axis length or the ellipticity can all beused to tell the degree of the measured astigmatism.

When a substantially good compensation of the sphero defocus componentoccurs, the resultant wavefront is equally divergent for half of theoverall wavefront (1214) and equally convergent for the other half ofthe overall wavefront (1224). The sequential rotation of the nowcircular 2D data point centroid trace will be reversed as compared tothat of the two large ellipses 1232 and 1236.

It is worth mentioning that although there is a difference between the2D centroid data point pattern as the defocus offset is tuned or scannedaround the “best focus” region and the cross sectional shape of a beamwith astigmatism that is being focused, the fact is, there is actually avery good correspondence and similarity between the two. This verysimilar behavior is a key feature of the present disclosure that makesthe presentation of the wavefront measurement result so easy for visioncorrection practitioners to understand. Let us assume that a beamderived from a point source near the fovea is coming out from an eyethat has nearsightedness and also astigmatism and that the beam getsfocused from right to left as shown at the bottom portion of FIG. 12.After leaving the eye, the beam will gets focused sooner in the verticaldirection than in the horizontal direction. This will make the beamcross section shape resemble a horizontal ellipse 1256.

At this moment, it should be reminded again that there is a differencebetween geometric ray optics which is an approximation and wave opticswhich is more accurate, in the sense that ray optics as shown in FIGS. 2and 4 assumes that a beam can be focused to an infinitely small size sothe curvature of a spherical wavefront will not change which is nottrue, but in reality, wave optics shows that as a convergent beam getsfocused, the wavefront will gradually transform from being convergentwith a relatively fixed radius of curvature as predicted by ray optics,to being more convergent, to being less convergent, to being planar andthen to being less divergent, being more divergent and finally to beingless divergent with a relatively fixed radius of curvature as predictedby ray optics. Accordingly during the transition, the radius ofcurvature of the wavefront will change from positively larger but moreconstant as predicted by ray optics to smaller to larger, to infinity,and to negatively larger to smaller to larger but with a relativelyfixed radius of curvature as predicted by ray optics. Note that in FIG.12, we are only presenting the case for the region near “best focus”which is not the ray optics theory still valid region.

So if we look at the vertical cross sectional wavefront, as it getscloser to its “best focus” position, it will become less convergentsooner than the horizontal cross sectional wavefront that is still farfrom its “best focus” position. This wavefront situation corresponds to1216 and 1226. It happens that the 2D data point pattern 1246 is also ahorizontal ellipse so there is a good correspondence.

As the astigmatic beam gets more focused, it becomes a horizontal line1255. This means that in the vertical direction, the beam is bestfocused. So the vertical cross sectional wavefront should be planar(1215) while the horizontal cross sectional wavefront is stillconvergent (1225). Note that the 2D centroid data point pattern 1235 isalso a horizontal line, so again there is a good correspondence.

As the astigmatic focusing beam propagates further, it turns into acircle of least confusion and the beam shape will be a circle 1254. Atthis location, the vertical cross sectional wavefront will have passedthe planar location and is becoming slightly divergent (1214), while thehorizontal cross sectional wavefront is still slightly convergent (1224)because it has not reached its “best focus” position. Correspondingly,there is a sequentially reversed circular 2D data point pattern 1234.

As the astigmatic focusing beam travels further, the beam shape becomesa vertical line 1253. Note that the vertical cross sectional wavefrontnow becomes more divergent (1213) while beam get perfectly focused inthe horizontal direction which means that the horizontal cross sectionalwavefront is planer (1223). Correspondingly, the 2D centroid data pointpattern is also a vertical line 1233.

With the astigmatic focusing beam propagating even further, the beamshape turns into a vertical ellipse (1252). At this position, thevertical cross sectional wavefront becomes even more divergent (1212)while the horizontal cross sectional wavefront is just becoming slightlydivergent (1222). It happens that the 2D data point pattern is also avertical ellipse (1232).

Combining the above discussion with that made for a sphericallyconvergent or divergent wavefront beam being focused and a planarwavefront beam, it can be seen that the goal of getting the 2D datapoint pattern to collapse together is also a good correspondence tofocusing a beam to a single point. So the 2D centroid data point patternobtained from a wavefront measurement by sampling around an annular ringof the wavefront of a beam can intuitively indicate the state ofemmetropia and the existence of spherical and cylindrical refractiveerrors in a manner that can be so easily understood by vision correctionpractitioners. So it should be understood that the unique way ofpresenting a wavefront measurement in the form of a 2D centroid datapoint pattern that has the similar properties as the shape of a beambeing focused is a key feature of an embodiment of the presentdisclosure.

As one aspect of an embodiment, a calibration wavefront measurement canbe made for a substantially planar wavefront to determine therelationship between the centroid trace parameters, the annular ringdiameter and width, and the defocus offset. Then a real measurement of awavefront from an eye can be made by scanning the defocus offset, andalso possibly the annular ring size in terms of its diameter and width,and relating the measurement results to the calibration data. In doingso, a more accurate measurement of both the spherical refractive errorand the cylindrical refractive error of an eye can be obtained.

Note that the same eye or optical element alignment and eye trackingconcept that has been discussed for the spherical refractive error casecan still be applied to an eye with both spherical and cylindricalrefractive errors. In this case, as the defocus offsetting device isscanned, the center of the ellipse (with the straight lines and thesequentially reverse circle as the extreme case of an ellipse) can becompared to the reference point and if the centers always land to withina predetermined distance from the reference point, it can be consideredthat good alignment or tracking has been achieved.

It should be noted that if the eye has higher order aberrations otherthan or in addition to defocus and astigmatism, the 2D data pointpattern will depart from an ellipse (with the circle and the straightline being two extreme cases of an ellipse). As one aspect of anembodiment, such a non-perfect elliptical data point pattern or centroidtrace can be either displayed directly or fitted to an ellipse and thedrifting off of the data points from a fitted ellipse will indicate tothe vision correction practitioner that there are higher orderaberrations. The amount of non-symmetric drift or variance from the bestfit ellipse can be used to assess the best nulled focus location withoptimal measurement of spherical nulling. This form of displaying higherorder aberrations will obviously be more acceptable and understandableto a vision correction practitioner than a 2D wavefront map or Zernikepolynomial coefficients. It should be noted, however, that whennon-symmetry is shown in the display, it can means a number of possiblecauses. For example, it can be caused by a misalignment of the eyerelative to the presently disclosed apparatus. Under such acircumstance, the actual spherical refractive error induced centroidpattern will most likely not be symmetric and symmetry should not beforced by alignment away from axis of fixation as otherwise incorrectastigmatism will be reported.

The most interesting feature about the two defocus offsets that resultin the two straight line shape of the 2D data point pattern is that theline can more clearly show the axis of the astigmatism. Meanwhile thelength of the straight lines combined with the amount of defocus candirectly indicate the degree or diopter value of the astigmatism.Although the length of the straight line is dependent on the annularring diameter or radius, and also to a certain extent, on the samplingaperture size, but these can be determined and calibrated in advance. Asone aspect of an embodiment, the defocus offsetting device can bescanned to find the two straight lines of the 2D data point patterns,such a scanning can be initiated by the vision correction practitioneror the refractive surgeon or by a built-in algorithm, and the defocusoffset can be stopped at one of the two values or positions to show thestraight line on the display. The defocus scanning will enable the enduser to achieve a more precise determination of the axis and amount ofastigmatism. The scanning of the defocus, and also possibly combinedwith the scanning of the annular ring, can also serve the purpose ofaveraging out noise and obtaining a better measurement of the aberrationof the eye. For example, the range between the two defocus offset valuesthat induce the two straight lines for the 2D data point pattern can beused to provide information about the astigmatism of the eye.

The two straight lines of the 2D data point pattern actually show thatone can correct the refractive errors using at least two combinations ofspherical and cylindrical lenses. The first combination is to use thedefocus offset value that resulted in the first (vertical) straight line1233 to select a spherical lens to correct the spherical refractiveerror. Such a spherical lens will make the horizontal cross sectionalwavefront 1223 planar. At the same time, since the vertical crosssectional wavefront 1213 is still slightly divergent, a positivecylindrical lens can be used to only focus light in the verticaldirection (more generally, the direction along the first straight line)to bring the vertically still slightly divergent wavefront to planarwavefront. As a result, the 2D centroid data points can all be broughtto the center and the overcall wavefront can be made completely planar.This will lead to a perfect correction of the spherical and cylindricalrefractive errors.

The second combination is to use the defocus offset value that resultedin the second (horizontal) straight line 1235 of the 2D centroid datapoint pattern to select a spherical lens to correct the sphericalrefractive error. Such a spherical lens will make vertical crosssectional wavefront 1215 planar. At the same time, since the horizontalcross sectional wavefront 1225 is slightly convergent, a negativecylindrical lens can be used to only negatively focus light in thehorizontal direction (more generally, the direction along the secondstraight line) to make the horizontally slightly convergent wavefront toplanar wavefront. As a result, the 2D centroid data points can all bebrought to the center and the overcall wavefront can be made completelyplanar. This will lead to another perfect correction of the sphericaland cylindrical refractive errors.

Besides these two combinations, there are also other combinationpossibilities. For example, if the defocus (spherical lens) correctioncorresponds substantially to the circle of least confusion case which issomewhere between the two straight lines, then the astigmatic correctionwould require a cylindrical lens with both positive and negativecylinder refractions respectively at two orthogonal orientationdirections. It is perhaps more practical to choose a thinner overalllens combination that corresponds to smaller diopter values for both thedefocus correction and the astigmatism correction. In some cases, thespherical correction can be that which corresponds to the circle ofleast confusion. To achieve this, the defocus offset can be scanned anda built-in algorithm can be used to find out the best fit to asequentially reversed circular 2D data point pattern by matching thelength of the major and the minor axis. This defocus offset will then bethe expected spherical correction and the diameter of the 2D data pointpattern circle can be used to determine the degree of the stillremaining astigmatism for the selection of a cylindrical lens with bothpositive and negative but orientation-wise orthogonal focusing powers.

Note that dynamically offsetting the defocus based on the real timewavefront measurement feedback will provide many advantages for eyeaberration measurement and vision correction. As an embodiment, when thedisclosed apparatus is used for determining the refractive errors of apatient's eye, the end user can enable the apparatus to scan the defocusoffsetting device and also change the patient's accommodation to obtaina more precise measurement of the refractive errors under differentaccommodation conditions. Changing the accommodation to find out thepatient accommodation range will enable the doctor to identify the rangeand also the far side of the accommodation and hence make the patient tofixate at a desired distance. Then the desired spherical and cylindricalrefractive corrections or even higher order aberration correctionprescription can be made based on the series of 2D data point centroidpatterns, such as one of the two 2D data point pattern straight lines,obtained by scanning the defocus.

A prescription can also be generated automatically using a built-inalgorithm that takes advantage of the scanning of the defocus and alsothe accommodation. For example, the defocus offset device can be firstlybriefly scanned to identify and assume an offset value that will enablewavefront to be measured from a patient to fall within the wavefrontsensor measurement range. Afterwards, the accommodation range of the eyecan be determined by scanning the internal fixation while the wavefrontsensor is monitoring the wavefront change. Within the accommodationrange, as the internal fixation is scanned, the eye will be able tocompensate so the measured real time wavefront will tend to restore tothe same state. However, when the internal fixation is scanned to theone of the two accommodation limits, the eye will no longer be able tocompensate for the internal fixation change, the eye is now ‘fogged”.Any further internal fixation scanning will render the eye notresponding and the real time wavefront measurement will show that theeye has reached one of the two accommodation limits In this way the twolimits of the eye's accommodation can be found. These processes can berun automatically by a built-in algorithm.

Following the determination of the accommodation range, the eye can bemade to fixate at far side of the accommodation limit. Then the defocusoffsetting device can be scanned to identify, for example, one of thetwo 2D centroid data point pattern straight lines. Again, this can bedone automatically by a built-in algorithm. Since there is apre-calibration, the length of the straight line and the orientationdirection will be able to provide a prescription of the cylindrical lensand the current defocus offset value should be able to provide aprescription of the spherical lens. The thus obtained lens prescriptionhas considered the accommodation range and will enable the patient tosee a distance object clearly and at the same time also be able to focusto clearly see an object that is as near as his accommodation rangeallows.

The prescription can be tested on the patient using trial lenses. Again,the patient's accommodation can be changed and the real time display ofthe 2D data point pattern will tell the end user if the visioncorrection is good or not. In addition, with the precision of awavefront measurement around different annular ring sizes and also witha control of the patient accommodation along the full accommodationrange, it is highly likely that the prescription thus obtained (thatcould have also considered higher order aberrations) will be far moreaccurate than what can be obtained using a simple autorefractor, andtherefore, there is a possibility that such a prescription will be goodenough to make the subjective confirmation no longer necessary.

As another aspect of an embodiment, a digital processor with a built-inalgorithm can be used to calculate and show the centration, themagnitude or the length as well as the orientation direction of angularaxis of the major and minor axes of the best fitted ellipse on thedisplay, thus directly telling the end user the spherical andcylindrical refractive errors of the wavefront being measured. Thedigital processor can also perform a best fit of the displayed 2D datapoint pattern to an ellipse and further guide the end user in finetuning the defocus offset so that an even more precise determination ofthe astigmatic axis can be achieved.

FIG. 13 shows an example flow chart of the major steps in finding themajor and minor axis and the spherical and cylindrical refractive errorsof the measured wavefront based on the 2D centroid data point pattern.As an option, the processor can also indicate the presence of higherorder aberrations relative to a predetermined criterion. The processorcan generate a signal to show the departure of the fitted ellipse to acircle or a collection of data points or a straight line and this signalcan be used to drive the wavefront offsetting element or device. Theinformation obtained can be displayed together with 2D centroid datapoint pattern in the wavefront display window. For example, at onecorner of the wavefront display window, real time refractive errors interms of the sphero-cylindrical diopter values and the astigmatism axisin degrees can be displayed together with the major and minor axislength of the best fit ellipse, the ratio of the two axis, and thepresence or absence of high order aberrations. In addition, during avision correction procedure, the real time information displayed can beautomatically digitally “zoomed out” or “zoomed in” to alert the visioncorrection practitioner that the correction is going in the wrong orright direction. When a certain level of correction has been reached,the displayed information can turn into a highlighted form in terms of,for example, font size, boldness, style or color.

Processing starts in process block 1302 and proceeds to block 1304 wherethe midpoint vector of the raw data point position vectors returned fromthe position sensors is computed. In processing block 1306 all the rawdata point position vectors are translated by the midpoint vector. Inprocess block 1308 the average length of the translated point vectors iscomputed to determine the average radius of an enclosing circle. Inprocessing step 1310 each translated point vector length is compared tothe average radius to select all point vectors having a vector lengthlarger than the selected radius.

In processing step 1313 a curve fitting algorithm is used to determinean orientation angle of a straight line that best fits the selectedpoint vectors. This angle is one of the axes of astigmatism. In processstep 1314 all translated points are rotated by the orientation angle toplace the major and minor axes orthogonal to an x,y coordinate system.

In process step 1316 the magnitudes of semi-major and semi minor axesare determined by curve fitting the rotated point vectors to the formulafor an ellipse. In process steps 1318 and 1320 the magnitudes of thesemi-major and semi-minor axes are used to compute the spherical andcylindrical refractive errors in diopters. As described above, thisinformation is provided to the user as a prescription for correctivelenses.

In process step 1322 the error from an ellipse is calculated to indicatethe presence of higher order aberrations which can be further analyzedto determine corrective measures.

In process step 1324, the minor axis length or the major over minor axislength ratio of the fitted ellipse can be used to determine if thefitted ellipse is close to circle or a data point or a straight line anda signal can be outputted to drive the wavefront offset element tochange the offset. Per a built-in algorithm or the input from the enduser, the process steps can be repeated until a desired fit to forexample a straight line is obtained. Finally, the process ends atprocess step 1326.

The algorithm can be implemented automatically by the microcontrollerexecuting firmware held in onboard memory. Alternatively, the programcode could be stored on the host and used to control the various controlmodules or some combination of host control and firmware could beutilized.

The displayed 2D data point pattern can also be digitally “zoomed in” or“zoomed out” to “magnify” or “de-magnify” the 2D data point pattern onthe display. This feature will be extremely useful for a real timevision correction procedure. The scanning of the defocus offset willenable the end user to find the two “straight lines” and hence the axisof the astigmatism. In conducting a real time correction of theastigmatism, the length of the two “straight lines” or the length of theellipse will shorten as the correction is being performed and at acertain stage, there will be a need to “zoom in” and fine tune thedefocus offset to see if the 2D data point pattern still resembles a“straight line”, until its disappearance and the achievement of a“perfect” circle or the complete clustering together of the data points.

The presently disclosed apparatus can be designed for ease of operationin several ways in terms of user interaction with the apparatus. First,patient demographic information can be entered into the system. Thisoccurs either by direct input of data through a computer keyboard, orvia established communication and security standards such as DICOM andHIPAA compliant services to an Electronic Medical Record that connectsvia an electronic network and communicates with an established interfacesuch as Health Language 7. Once the patient demographics are loaded intothe device, a number of other parameters are selected. Any of the inputsfrom the user can be performed by a variety of paradigms, includingkeyboard, touch screen, voice, virtual reality gloves, and footswitch.The parameters that can be entered initially include operative eye,procedure being performed (e.g. toric, multifocal, or accommodatingintraocular lens [IOL] implantation), cylinder to display in plus orminus configuration, recording of data on/off, audio feedback on/off,and heads-up display on/off.

Once the above information has been entered, the system is ready tobegin use. The surgeon then completes the cataract extraction, and priorto IOL insertion, begins measuring the aphakic eye's wavefront. Thedeterministic dynamic wavefront sensing system is turned on via one ofthe modalities mentioned above as mechanisms of interaction with thedevice. Then, after the surgeon implants the IOL, the measurement of thewavefront continues. The surgeon adjusts the IOL position in the eyeuntil the measurement confirms optimal placement of the IOL. Once thesurgery is complete, the data is saved (if recording of data was turnedon) and the system is switched off.

As an application embodiment, the presently disclosed apparatus can beused in cataract surgery to optimize the implantation of a conventionalintra ocular lens (IOL). Initially, when the crystal lens is removedfrom the eye, the presently disclosed apparatus can be used to confirmthe aphakic condition throughout the entire corneal visual field throughdynamically changing the annular ring size. With an IOL implanted, asthe defocus offset is tuned, the digital gain of the 2D data pointposition relative to origin of the x-y coordinate system on the displaycan also be increased or decreased to enable the end user to “zoom in”and “zoom out” and hence “magnify” or “de-magnify” the 2D data pointpattern. In the case of a pure spherical refractive error correction, bychanging the defocus offset, the diameter of a circle-like 2D data pointpattern can be controlled by the end user to ease the centering of the2D data point pattern relative to a reference point (such as the origin)of the x-y coordinate system and hence to achieve a better positioningaccuracy of the IOL in the eye. The circle size can be changed per theneed of the refractive surgeon by changing the defocus offset as well ascontrolling the digital “zooming”, and as a result, the positioningprecision of the implanted IOL can be substantially improved by movingthe IOL until the circular 2D data point pattern is centered withrespect to the reference point (such as the origin) of the coordinateaccording to some predetermined criteria. The “closing in” or“collapsing” of the scattered data points, especially with the help ofthe “zooming in” function through a digital gain control will help thefine positioning of the IOL, and at the same time the drive signal thatcorresponds to the best “zoomed in” closing of the data points willprecisely indicate if the correction of the spherical refractive erroris precisely achieved. This process of finding the best centeringposition can be automated also using a built-in algorithm.

As still another application embodiment, the presently disclosedapparatus can be used to indicate if an implanted multi-focal IOL hasthe desired focusing range in addition to optimizing its positioning. Asis known to those skilled in the art, a multi-focal lens usually has anumber of concentric annular zones with each annular ring having adifferent focusing power. Generally, as the zone gets further away fromthe center and closer to the outer peripheral region, the width of theannular ring gets narrower. In US20080278683, it has been mentioned thatby using an adaptive sequential wavefront sensor to do the wavefrontmeasurement, one can adjust the sampled annular ring diameter and theannular ring width by controlling the scan mirror tilt angle and thesub-wavefront sampling aperture size so that the sampled subwavefrontscan be made to match with the different annular zones of the implantedmulti-focal IOL. The presently disclosed apparatus can therefore be usedto measure the wavefront from each annular zone individually and a livedisplay/feedback of the measurement result combined with a properdefocus offset and also if needed, with accommodation change, can tellthe refractive surgeon if the desired spherical refractive errorcorrection for a particular zone is achieved. When the focusing power ofeach individual zone is obtained, the overall focusing range of theimplanted multi-focal lens can also be determined. The surgeon willtherefore be able to tell if the surgery is successful in terms ofincreasing the focusing range of the patient to the specified degree orextent.

As a key application embodiment, the presently disclosed apparatus canbe used to optimize the implantation and orientation of a toric IOL. Inimplanting a toric IOL during a cataract refractive surgery, in additionto the centering and tilt optimization of the toric IOL, a critical stepis in rotating of the toric IOL to a desired orientation axis so that acomplete correction of astigmatism can be achieved. The digital “zoomin” feature can become most useful for the toric IOL implantationprocedure. FIG. 14 shows a schematic diagram of a toric IOL that hasaxis marks. As one aspect of an embodiment, the defocus can be offset toturn the 2D data point pattern on a display into a straight line and asa result, any remaining astigmatism can be shown with more detail. Atthis stage, the implanted toric lens can be rotated so that thedisplayed 2D data point straight line is turned into a circle. Thedefocus can then be further tuned to further try to turn the 2D datapoint display into a straight line and the “zoom in” feature can now beutilized while the toric IOL is being further rotated to change thestraight line to a circle. This process can be repeated until a certainpredetermined criterion has been reached. By rotating the implantedtoric IOL to convert the straight line or ellipse to a circle and alsofine tune the defocus with digital “zooming in” to make sure that thecircle can be “closed” at the reference point or origin of the x-ycoordinate, the desired position and angular orientation of theimplanted toric IOL can be more precisely surgically determined

As still another application embodiment, the presently disclosedapparatus can be used to check if an implanted accommodating oraccommodative intra ocular lens (AIOL) can provide the desiredaccommodation range. As is well known to those skilled in the art, anAIOL is a lens that can change its focusing power in the eye under theaction of the ciliary muscle. During AIOL implantation, in addition tocentering the AIOL, if the ciliary muscle can still function, thepatient can be made to accommodate at different distances with the helpof the variable internal fixation. Otherwise, other ciliary musclestimulation mechanism can be used to enable the accommodation change. Byscanning the defocus offset and also doing a real time wavefrontmeasurement, a more accurate measurement of the refractive errors alongthe full accommodation range of the implanted AIOL can be obtained. Thiswill indicate whether the desired ciliary muscle enabled accommodationrange has been reached with the implantation of the AIOL. The samemeasurement can also be done after the surgical operation when thepatient has restored his/her accommodating capability.

As another application embodiment, the presently disclosed apparatus canalso be used to provide a therapy for presbyopia, and to maximizesurgical results after AIOL implantation. It is known to those skilledin the art that the inherent physiologic mechanism of accommodation isthe same both for natural accommodation and for AIOLs. The capability ofthe presently disclosed apparatus to detect changes in the accommodationof the patient while obtaining real time wavefront measurement resultsmay be used via a biofeedback mechanism to the patient, to enhanceresidual capabilities and thereby to delay the onset of presbyopia andto treat presbyopia once it begins.

After a surgery, a patient with an implanted AIOL can also utilizereal-time biofeedback information to enhance the functioning of the lensthrough psychophysical feedback. In other words, the apparatus canrecord the complete optical condition of the eye in real-time, collectand analyzes the data and feedback the results to the patient tomaximize performance of AIOL. The feedback can be derived based onreal-time wavefront information and real-time measurement of theaccommodation range or amplitude. The feedback can also be in the formof raw data, derived maps of information related to amplitude ofaccommodation, and/or other sensory inputs controlled by maximizingaccommodation (including visual, auditory, olfactory, tactile, and/orgustatory feedbacks).

As still another application embodiment, the presently disclosedapparatus can be used to shape and position corneal onlay or inlay. Itis well known to those skilled in the art that a biocompatible materialcan be implanted as an inlay or onlay into or onto the cornea and can beablated with either excimer or femtosecond laser energy, or by otherprecise ablation technology. Such an ablation can enable an accurate andreversible refractive procedure that can eliminate the complications ofectasia and possibly post-op dry eye. The presently disclosed apparatuscan thus be used to optimize the ablation or the manufacturing of theinlay or onlay to achieve optimal visual performance. The modificationto the “blanks” can be performed either before or after implantationinto or on the eye. There are many possible materials that can be used,including artificial collagen, with or without cross linking,potentially being cross linked into the surgical bed of the patient'scornea, or various hydrogels and advanced polymers. The specificationsof the material can be determined to optimize function with real-timewavefront measurement as well as biocompatibility, reversibility,subsequent refinement, and optical performance. For example, thespecification of the material can be set such that it can be modifiedand/or manufactured with a relatively inexpensive technology (e.g. laseror electromagnetic radiation of any optimal wavelength that can bedelivered safely ex-vivo since there is no interaction with thepatient's eye, and is much less expensive than excimer or femptosecondlasers).

The real-time wavefront data provided by the presently disclosedapparatus can be used to measure the eye aberrations, performclosed-loop real-time ablation or creation of the inlay or onlay ex-vivo(both anterior and posterior surfaces), and then implant the productunder real-time intra-operative wavefront validation for accuratepositioning. In this manner, the patient's eye is never exposed to laserirradiation, and the procedure is completely reversible. The inlay oronlay can be removed completely, with a new implant performed.Alternatively and in addition, refinement surgery can be performed onthe inlay or onlay material at any time in the future. As anotheroption, the inlay or onlay can be put into place first, and then realtime wavefront data can be used to perform closed-loop real-timeablation of the inlay or onlay in-vivo. Clinically, all these approachesresult in a reversible procedure that is enabled through real-time andaccurate wavefront measurement provided by the presently disclosedapparatus. The intra-operative portion of the procedure is made possiblethrough accurate positioning of the inlay or onlay using the presentlydisclosed apparatus. The additional clinical advantage with ex-vivoprocedure is that energy is not delivered to the eye, and this willreduce the incidence of post-op dry eye or other post-op complications.

FIG. 15 shows a schematic diagram of another embodiment in which adynamic wavefront manipulation device is used to offset some selectedaberration components of the wavefront from an eye. The light sourcemodule 1535, the infrared imaging module 1583, the internalfixation/visual acuity projection module 1542, the real time wavefrontsensor module 1528, the electronic control and detection module 1532,and the display module 1592, serve a similar function as 535, 583, 542,528, 532, and 592 shown in FIG. 5. The light source module 1535,comprising the light source 1534, the collimating lens 1537 and the beamdirecting element 1536, is used to direct a narrow beam of light ontothe retina of a patient eye 1538. It should be noted that some of thesemodules are not absolutely required for the functioning of the apparatusas have been discussed before. In FIG. 15, besides the active defocusoffset element 1505, a wavefront manipulation module 1550 is added,which in FIG. 15 is shown as a deformable mirror 1552. The reason forthe inclusion of the defocus offset element 1505 in addition to thedeformable mirror 1552 is that generally speaking a deformable mirrorhas relative small stroke which means that its defocus offsetting rangeis limited. Therefore, a combination of a deformable mirror with adefocus offsetting element will enable one to achieve wavefrontmanipulation over a large practical range as the defocus or sphericalrefractive error variation is the largest of all wavefront aberrationsamong different eye. However, it should be noted that if the wavefrontmanipulation module 1550 does have a high enough dynamic range, thenthere is no need for the defocus offset element 1505. So the defocusoffset element 1505 is not an absolutely required element for thefunction of embodiment shown in FIG. 15.

Note that the embodiment shown in FIG. 15 is an extension of what isshown in FIG. 5. The concept is to offset some wavefront aberrationcomponents based on a real time wavefront measurement feedback in orderto allow the remaining aberration components to show up more clearly.The difference between the embodiment of FIG. 15 and that disclosed inUS20080278683 is that a wavefront manipulation module 1550 is arrangedin the light path to provide offset. Previous embodiments only mentionedthe compensation or nulling function of such an element. In the currentembodiment, in addition to the compensation or nulling function, thewavefront manipulation module 1550 also provides active off-setting orpartial compensation of only certain aberration components of awavefront from the patient's eye. The active offset is at the disposalof the refractive surgeon or controlled by a built-in algorithmaccording to the real time display and/or feedback of the wavefrontmeasurement. One aspect of the present embodiment is to scan the offsetof certain aberration components within the wavefront measurement rangewith or without the accommodation change of the eye over theaccommodation range so that a better and more precision measurement ofthe eye aberrations can be obtained.

It should be noted that although a deformable mirror is shown as thewavefront manipulation element in FIG. 15, other wavefront manipulationelement can be used, including transmissive liquid crystal basedwavefront manipulation device. One unique advantage of combining atransparent wavefront manipulator or corrector with a real timewavefront sensor is that one can achieve a really compact adaptiveoptics system.

The position of the wavefront manipulation element can be anywhere alongthe optical path as long as it serves the function of offsetting someselected wavefront aberration components. In fact, for a compact designthe wavefront manipulation element can be designed together with otheroptical element(s) inside the wavefront sensor 1528. Such a real timeadaptive optics sequential wavefront sensor can be made with a smallform factor and thus integrated into a large number of optical imagingor measurement systems, such as a refractive surgical microscope. Itshould also be noted that although a sequential wavefront sensor 1528has been illustrated in FIG. 15, other types of wavefront sensors canalso be used as long as it can provide wavefront measurement, includingHartmann-Shack, Talbot-Moire, Tscherning, Ray-tracing, phase diversityand interferometric wavefront sensors.

An independent form of wavefront recognition and control is an intrinsiccomponent of the presently disclosed device in that a separate opticalpath comprised of a local wavefront manipulator interacts with thereturn beam as a separate action in reducing and re-composing of thetransported beam aberrations to produce defined measurements of thelocal slope changes carried within the return beam. The activemanipulator introduces a local beam deflection or deformation that“matches” the opposite sign of the input beam thereby canceling out theoriginal beam deflection as the beam is sensed and measured. The activebeam manipulator has then captured the nature of the beam aberrationsallowing an active sensing and isolation of each defined variableaberration. This then provides the capabilities of introducing ornulling certain of the aberrations with respect to all or selectedexisting aberrations. In this active on-going process the deterministicdynamic wavefront sensing system can then provide a basis forinterrogating the relative impact of the existing aberrations on theactive performance of the system being evaluated. The active localwavefront manipulator has the capability of an independent operation forboth global and local facets of the aberration. The manipulator can beused in tandem with the linear spherical compensation optics to fullyenhance and provide ranging measurement capabilities while activelyevaluating the detailed composition of the wavefront irregularities.

The presently disclosed apparatus shown in FIG. 15 can provide real timewavefront measurement results and therefore be used to optimizeintra-operatively those refractive surgical procedures that can correcthigher order aberrations. For example, in the future, an IOL can becustom designed to correct higher order aberrations such as coma and insuch a case, when such an IOL needs to be implanted into an eye, therewill be a need to position it properly during the implantation. Anapparatus as shown in FIG. 15 can be used to compensate for example theastigmatism while offsetting the defocus. As a result, higher orderaberrations such as coma can be more clearly revealed in the 2D datapoint pattern with a certain defocus offset. The refractive surgeon canthen fine tune the position of the higher order aberration correctionIOL to ensure that the correction for higher order aberration isoptimized. There may be cases in which the high order aberrations needto be corrected through laser ablation of the corneal tissue while thelower order aberration is to be corrected by implanting a toric IOL.This approach can benefit a cataract patient with both low order andhigh order eye aberrations. By correcting the lower order aberrationswith a toric IOL, which typically is performed during cataract surgery,the corneal tissue material that is to be ablated to only correct higherorder aberrations will be much less than that needed if all theaberrations are corrected by ablating the cornea.

All refractive surgical procedures that can correct higher orderaberrations including LASIK, SBK, LTK, IntraLasik, FlEXi Lasik, PRK,LASEK, RK, LRI, CRI, and AK, can benefit from the presently disclosedapparatus. For these procedures, the wavefront can be sampled accordingto any sampling pattern so that information on some particular wavefrontaberration components can be obtained. The whole wavefront can becovered and higher order aberration (HOA) content, such as coma, whichis a very prevalent HOA that surgeons are becoming familiar with andhave ways to deal with, can be highlighted and displayed in a formateasily understandable by clinical practitioners. In fact, measurement ofasymmetric aberrations under good centration conditions, or anycollection of data points that did not track with a circle or ellipse ora line with inflections, would mean that there are other HOA causedeffects. The presence of these asymmetric conditions should be the normnot the exception since HOA will always be present to a certain extent.Understanding and separating these terms from sphero-cylindricalcondition will aid in assessing the practical surgical limits. Theremoval of these terms will allow a better understanding on how asurgery should be performed properly. This is of paramount importanceand essentially will set the presently disclosed apparatus apart fromall other current approaches.

As one aspect of an embodiment, the presently disclosed apparatus can becombined with any refractive surgical laser systems to provide real timewavefront measurement feedback and guide a refractive surgeon inoptimizing the refractive procedure. For example, when a certain higherorder aberration is orientation specific, offsetting some aberrationswill highlight the orientation dependence of the high order aberrationand with a real time wavefront measurement feedback, any otherwiseundetected cyclotorsional movements of the eye, or rotationalmisalignment between the eye and laser can then be detected and theorientation corrected and confirmed (based on pre-op assessments). Asanother example, it is known that there can be post-operative decreasein contrast sensitivity resulting from induced higher order aberrationsduring corneal refractive procedures (such as LASIK). In order tominimize this unfavorable and negative outcome, the presently disclosedapparatus can be used to provide a real time wavefront measurement withpartial compensation of lower order aberrations, thus enabling arefractive surgeon to clearly see if there are higher order aberrationsthat result during the laser ablation process and to minimize thesehigher order aberrations.

The presently disclosed apparatus can be incorporated into or combinedwith other ophthalmic devices as well to enhance their functionality. Inaddition incorporating such an apparatus in a surgical microscope tooptimize a cataract refractive surgery, as another aspect of anembodiment, the same apparatus can also be combined with a standard slitlamp to provide both real time wavefront measurement and a slit lampexamination of a patient's eye.

For example, imagine that in the operating room at the end of a cataractcase, the surgical microscope also captures a final wavefrontmeasurement of the eye after IOL implantation. If there is residualastigmatism, the surgeon can perform either a limbal relaxing incision(LRI) or corneal relaxing incision (CRI) with the real time wavefrontfeedback to titrate the incision until the desired neutralization ofastigmatism is achieved. Then, as the patient returns for follow upvisits, a slit lamp that is combined with a real time wavefront sensoras disclosed here will re-measure the same eye. The system will then beable to register the data from clinic measurement with the post-opmeasurement from the operating room at the end of the case, and look forregression over time. Based on the regression, the surgeon may recommend“enhancement” treatment, either back in the operating room, or in theclinic at the slit lamp. The clinic enhancement can be done under thesame real time wavefront sensor's guidance as was available in theoperating room. The titration of the enhancement procedure in the cliniccan be under continuous real-time feedback, providing better outcomes,and developing a physician specific database of wavefront guided limbalrelaxing incision (LRI) or corneal relaxing incisions (CRI) andintrastromal lenticule laser (Flexi) for further cylinder correction.

The above described embodiments can be used in a variety ofapplications. For example, it can be used in a lensometer to measure andfine tune the refractive power of a lens including a spectacle lens, acontact lens, and/or an IOL. Although various embodiments thatincorporate the teachings of the present invention have been shown anddescribed in detail herein, those skilled in the art can readily devisemany other varied embodiments that still incorporate these teachings.

1. An apparatus comprising: a dynamic wavefront sensor configured toreceive a portion of a wavefront and output position values indicatingthe position of focused subwavefronts, with the portion of the wavefrontcomprising a plurality of subwavefronts; a controllable wavefrontoffsetting element positioned to intercept the portion of the wavefrontbefore it is incident on the wavefront sensor; and a controller, coupledto the controllable wavefront offsetting element, configured to controlthe controllable wavefront offsetting element to offset selectedwavefront aberration components of the wavefront in order to allowremaining aberration components of the portion of wavefront to be moreefficiently detected
 2. The apparatus of claim 1 where the controllablewavefront offsetting element comprises: a lens combination thatintroduces spherical refractive offset into the portion of thewavefront.
 3. The apparatus of claim 2 where the controllable wavefrontoffsetting element comprises: a positive negative lens combination withrelative axial movement; with the controller further configured tocontrol the axial movement.
 4. The apparatus of claim 1 where thecontrollable wavefront offsetting element comprises: a dynamic wavefrontmanipulation device for offsetting selected aberration components of theportion of the wavefront: and with the controller further configured tocontrol the dynamic wavefront manipulation device.
 5. The apparatus ofclaim 1 further comprising: an internal fixation/visual acuity modulepositioned to project a pattern onto the retina of a patient's eye. 6.The apparatus of claim 1 where the position values indicate the x and yvalues of the focused subwavefront from a reference point being theposition value of the subwavefront of plane wave and further comprising:a display configured to display data points representing the positionvalues relative to the reference point.
 7. The apparatus of claim 6where the controller has a user input interface and further comprising:a user input device, coupled to the user input, for providing inputs tocontrol the wavefront offsetting element to controllably cancel part ofthe aberrations of the input wavefront.
 8. The apparatus of claim 1 withthe dynamic wavefront sensor comprising: a sub-wavefront focusing lensconfigured to focus a sub-wavefront to an image spot located on a focalplane; a sequential wavefront scanning device configured to sequentiallyproject sub-wavefronts, located on an annular ring of the portion of thewavefront, onto the sub-wavefront focusing lens; a variable apertureconfigured to control the size of a focused sub-wavefront; a positionsensing device, located substantially at the focal plane of thesub-wavefront focusing lens, configured to indicate the location of theimage spot on the focal plane; and with the controller, further coupledto the position sensing device, variable aperture, further configured tocoordinate the operation of the position scanning device and thevariable aperture.
 9. The apparatus of claim 8 where: the positionsensing device measures the tilt of a sub-wavefront as a displacement ofa centroid of a focused sub-wavefront incident on the position sensingdevice.
 10. The apparatus of claim 9 further comprising: a displayconfigured to display data points indicating the position valuesrelative to the reference point.
 11. An apparatus comprising: asub-wavefront focusing lens configured to focus a sub-wavefront, beingan incident portion of a wavefront generated by a light source, to animage spot located on a focal plane; a sequential wavefront scanningdevice configured to sequentially project different portions of anincident wavefront on the sub-wavefront focusing lens; a variableaperture configured to control the size of the sub-wavefront; a positionsensing device, located substantially at the focal plane of thesub-wavefront focusing lens, configured to indicate the location of theimage spot on the focal plane; a controllable wavefront offsettingelement positioned to intercept the portion of the wavefront before itis incident on the wavefront sensor; and a controller, coupled to thecontrollable wavefront offsetting element, configured to control thecontrollable wavefront offsetting element to offset selected wavefrontaberration components of the wavefront in order to allow remainingaberration components of the portion of wavefront to be more efficientlydetected.
 12. The apparatus of claim 11 where the controllable wavefrontoffsetting element comprises: a lens combination that introducesspherical refractive offset into the portion of the wavefront.
 13. Theapparatus of claim 12 where the controllable wavefront offsettingelement comprises: a positive negative lens combination with relativeaxial movement; with the controller further configured to control theaxial movement.
 14. The apparatus of claim 11 where the controllablewavefront offsetting element comprises: a dynamic wavefront manipulationdevice for offsetting selected aberration components of the portion ofthe wavefront; and with the controller further configured to control thedynamic wavefront manipulation device.
 15. The apparatus of claim 11where the controller is further configured to control the variableaperture.
 16. A method comprising: sampling subwavefronts from awavefront returned from the retina of the eye with a wavefront sensor,where the wavefront is a portion of a narrow beam of light directed tothe retina of the eye and returned to the wavefront sensor and with thesubwavefronts disposed on an annular ring portion of the wavefront;measuring, using the wavefront sensor, position values for eachsubwavefront, where each position value indicates the offset of afocused subwavefront centroid from a reference point being the positionof the centroid of a reference plane wave wavefront and where thewavefront sensor outputs position values in real-time; changing, using aprocessor, the spherical refractive offset, introduced into thewavefront by a controllable wavefront offsetting element, in a firstdirection to a first selected offset position, with the controllablewavefront offsetting element positioned to intercept the wavefrontbefore the wavefront is incident on the wavefront sensor and where thecontrollable wavefront offsetting element introduces a controllablespherical refractive offset into the wavefront; computing, using theprocessor, Cartesian coordinates of measured position values at acurrent offset position; displaying a shape comprising a trace of thecurrent position values as data points on a display; computing, usingthe processor, parameters relating to the ellipticity of a displayedshape; computing, using the processor, values of wavefront tilts at thecurrent offset position; if the value of the wavefront tilt is withinthe dynamic range of the wavefront sensor, changing, using theprocessor, the spherical refractive offset, introduced into thewavefront by a controllable wavefront offsetting element, in the firstdirection to a second selected offset position; computing, using theprocessor, Cartesian coordinates of measure position values at a firstcurrent offset position; displaying a shape comprising a trace of thecurrent position values as data points on a display; computing, usingthe processor, parameters relating to the ellipticity of a displayedshape; computing, using the processor, values of wavefront tilts at thecurrent offset position; if the value of the wavefront tilt is outsidethe dynamic range of the wavefront sensor terminating scanning in acurrent direction; and from the ellipses obtained by scanning theoffset, determining the best offset value from the ellipses obtained byscanning that can highlight remaining aberrations; and returninginformation to a refractive surgeon on how to best continue a visioncorrection procedure.
 17. A method comprising: sampling subwavefrontsfrom a wavefront returned from the retina of the eye with a wavefrontsensor, where the wavefront is a portion of a narrow beam of lightdirected to the retina of the eye and returned to the wavefront sensorand with the subwavefronts disposed on an annular ring portion of thewavefront; measuring position vectors for each subwavefront, using thedynamic wavefront sensor, where each position vector indicates theoffset of a focused subwavefront centroid from a reference point beingthe position of the centroid of a reference plane wave wavefront andwhere the wavefront sensor outputs position values in real-time;computing a midpoint vector, using a processor, of raw position vectorsoutput by the wavefront sensor; translating, using the processor, allthe raw position vectors by the midpoint vector; computing, using theprocessor, the average length of translated position vectors todetermine the average radius of an enclosing circle; comparing, usingthe processor, each translated position vector length to the averageradius to select all position vectors having a vector length larger thanthe selected radius; curve fitting, using the processor, all selectedposition vectors to determine an orientation angle of a straight linethat best fits the selected position vectors, where the orientationangle is one of the axes of astigmatism; rotating, using the processor,all translated position vectors by the orientation angle to place themajor and minor axes orthogonal to an x,y coordinate system;determining, using the processor, the magnitudes of semi-major and semiminor axes by curve fitting the rotated point vectors to the formula foran ellipse; computing, using the processor, the spherical andcylindrical refractive errors in diopters using the magnitudes of thesemi-major and semi-minor axes; computing, using the processor, theerror from a fitted ellipse to indicate the presence of higher orderaberrations which can be further analyzed to determine correctivemeasures; and determining, using the processor, the minor axis length orthe major over minor axis length ratio of the fitted ellipse todetermine if the fitted ellipse is close to circle or a data point or astraight line; and outputting, using the processor, a signal to changethe spherical refractive offset, introduced into the wavefront by acontrollable wavefront offsetting element, to change the sphericalrefractive offset so the fitted ellipse is closer to a circle or a datapoint or a straight line.